feat(career): CV builder backend — data-driven theme engine + variant model

Phase 4 foundation. A CvVariant is a lens over the master CareerProfile
(section order/visibility, per-item overrides keyed by ItemKey, theme +
builder settings) — it references career data, never duplicates it. One
renderer (ThemedCvRenderer) draws every theme; a theme is pure data
(CvThemeCatalog, 8 professional themes), so adding a theme needs no renderer
change. Autosave version history + non-destructive restore, public CV via
/api/public-cv/{slug} (anonymous, noindex, filter-bypassing owner load), and
an AI-assist endpoint reusing the existing provider abstraction (suggestions
only, never auto-applied).

- Models: CvVariant/CvVariantVersion, CvVariantSettings, CvTheme + catalog
- Services: CvVariantResolver (profile+lens -> render model), ThemedCvRenderer,
  CvVariantService, CareerProfileService.LoadStructuredForOwnerAsync (public)
- API: CvVariantController (/api/cv), PublicCvController (/api/public-cv)
- Migration AddCvVariants (2 self-contained tables; verified applied on the
  running container), 16 tests (resolver/renderer/service), 296 backend green

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Models/CvTheme.cs

@@ -0,0 +1,145 @@
+namespace JobTrackerApi.Models;
+
+// A theme is DATA, not code. The renderer (ThemedCvRenderer) has one render path; every visual
+// difference between themes is expressed by the fields below. Adding a theme = adding one CvTheme to
+// CvThemeCatalog — no renderer changes. This is the core Phase 4 architectural rule
+// ("Do NOT hardcode HTML templates"). docs/architecture/cv-theme-engine.md.
+public sealed class CvTheme
+{
+    public string Id { get; init; } = string.Empty;
+    public string Name { get; init; } = string.Empty;
+    public string Category { get; init; } = string.Empty;
+    public string Description { get; init; } = string.Empty;
+
+    // single | sidebar-left | sidebar-right | header-band
+    public string Layout { get; init; } = "single";
+    public double SidebarWidthMm { get; init; } = 62;
+
+    // Palette
+    public string Accent { get; init; } = "#2563eb";
+    public string Ink { get; init; } = "#111827";
+    public string Muted { get; init; } = "#4b5563";
+    public string Line { get; init; } = "#d1d5db";
+    public string Paper { get; init; } = "#ffffff";
+    public string SidebarBg { get; init; } = "#f3f4f6";
+    public string SidebarInk { get; init; } = "#111827";
+    public string? HeadingColor { get; init; } // null => accent
+
+    // Typography
+    public string HeadingFont { get; init; } = "Georgia, 'Times New Roman', serif";
+    public string BodyFont { get; init; } = "Arial, Helvetica, sans-serif";
+    public double NameSizePt { get; init; } = 24;
+    public double HeadingSizePt { get; init; } = 12;
+    public double BodySizePt { get; init; } = 10;
+    public double LineHeight { get; init; } = 1.42;
+
+    // Spacing (mm)
+    public double PageMarginMm { get; init; } = 16;
+    public double SectionGapMm { get; init; } = 6;
+    public double EntryGapMm { get; init; } = 4.5;
+
+    // plain | band | centered | kicker
+    public string HeaderStyle { get; init; } = "plain";
+    // caps-rule | underline | plain | bar
+    public string HeadingStyle { get; init; } = "caps-rule";
+    // none | square | rounded | circle
+    public string PhotoShape { get; init; } = "rounded";
+
+    public bool DefaultIcons { get; init; }
+
+    // Which section keys render in the sidebar for two-column layouts (ignored for single/header-band).
+    public List<string> SidebarSections { get; init; } = new() { "contact", "skills", "languages" };
+}
+
+public static class CvThemeCatalog
+{
+    // 8 professional themes, all data. To add one: append here.
+    public static readonly IReadOnlyList<CvTheme> Themes = new List<CvTheme>
+    {
+        new()
+        {
+            Id = "modern", Name = "Modern", Category = "Modern Professional",
+            Description = "Clean SaaS-style layout with a confident accent header.",
+            Layout = "header-band", HeaderStyle = "band", HeadingStyle = "caps-rule",
+            Accent = "#2563eb", HeadingFont = "'Segoe UI', Roboto, Arial, sans-serif", BodyFont = "'Segoe UI', Roboto, Arial, sans-serif",
+            PhotoShape = "rounded", DefaultIcons = true,
+        },
+        new()
+        {
+            Id = "minimal", Name = "Minimal", Category = "Minimal",
+            Description = "Quiet, spacious, typography-first. Nothing competes with the content.",
+            Layout = "single", HeaderStyle = "plain", HeadingStyle = "plain",
+            Accent = "#111827", HeadingColor = "#111827", Muted = "#6b7280",
+            HeadingFont = "'Helvetica Neue', Arial, sans-serif", BodyFont = "'Helvetica Neue', Arial, sans-serif",
+            SectionGapMm = 7, EntryGapMm = 5, PhotoShape = "none",
+        },
+        new()
+        {
+            Id = "executive", Name = "Executive", Category = "Executive",
+            Description = "High-contrast, serif, leadership-weighted. For senior and client-facing roles.",
+            Layout = "single", HeaderStyle = "centered", HeadingStyle = "underline",
+            Accent = "#7c2d12", Ink = "#1c1917", Muted = "#57534e", Line = "#1c1917",
+            HeadingFont = "Georgia, 'Times New Roman', serif", BodyFont = "Georgia, 'Times New Roman', serif",
+            NameSizePt = 27, PhotoShape = "square",
+        },
+        new()
+        {
+            Id = "technical", Name = "Technical", Category = "Technical",
+            Description = "Dense two-column layout tuned for engineering CVs — skills and projects up front.",
+            Layout = "sidebar-left", HeaderStyle = "band", HeadingStyle = "bar",
+            Accent = "#0f4c5c", Ink = "#102a43", Muted = "#486581", SidebarBg = "#0f4c5c", SidebarInk = "#ffffff",
+            HeadingFont = "'Roboto', Arial, sans-serif", BodyFont = "'Roboto', Arial, sans-serif",
+            BodySizePt = 9.5, LineHeight = 1.36, DefaultIcons = true,
+            SidebarSections = new() { "contact", "skills", "languages", "certifications" },
+        },
+        new()
+        {
+            Id = "ats-classic", Name = "ATS Classic", Category = "ATS Professional",
+            Description = "Single column, no graphics, maximum parser compatibility. The safe default.",
+            Layout = "single", HeaderStyle = "plain", HeadingStyle = "caps-rule",
+            Accent = "#334155", Ink = "#111827", Muted = "#374151",
+            HeadingFont = "Arial, Helvetica, sans-serif", BodyFont = "Arial, Helvetica, sans-serif",
+            PhotoShape = "none",
+        },
+        new()
+        {
+            Id = "nordic", Name = "Nordic", Category = "Modern Professional",
+            Description = "Calm cool-blue sidebar, generous whitespace, Scandinavian restraint.",
+            Layout = "sidebar-right", HeaderStyle = "plain", HeadingStyle = "caps-rule",
+            Accent = "#3b6ea5", Ink = "#1f2937", Muted = "#4b5563", SidebarBg = "#eef3f8", SidebarInk = "#1f2937",
+            HeadingFont = "'Segoe UI', Arial, sans-serif", BodyFont = "'Segoe UI', Arial, sans-serif",
+            PhotoShape = "circle", DefaultIcons = true,
+        },
+        new()
+        {
+            Id = "elegant", Name = "Elegant", Category = "Creative",
+            Description = "Editorial serif headings over sans body, premium spacing and a plum accent.",
+            Layout = "single", HeaderStyle = "kicker", HeadingStyle = "underline",
+            Accent = "#7c3aed", Ink = "#1f2937", Muted = "#4b5563",
+            HeadingFont = "Georgia, 'Times New Roman', serif", BodyFont = "'Segoe UI', Arial, sans-serif",
+            NameSizePt = 26, SectionGapMm = 7, PhotoShape = "circle",
+        },
+        new()
+        {
+            Id = "creative", Name = "Creative", Category = "Creative",
+            Description = "Bold accent sidebar and photo-forward header for design and product roles.",
+            Layout = "sidebar-left", HeaderStyle = "band", HeadingStyle = "bar",
+            Accent = "#db2777", Ink = "#18181b", Muted = "#52525b", SidebarBg = "#db2777", SidebarInk = "#ffffff",
+            HeadingFont = "'Poppins', 'Segoe UI', Arial, sans-serif", BodyFont = "'Segoe UI', Arial, sans-serif",
+            PhotoShape = "circle", DefaultIcons = true,
+            SidebarSections = new() { "contact", "skills", "languages", "interests" },
+        },
+    };
+
+    public static CvTheme Resolve(string? id)
+    {
+        var key = (id ?? string.Empty).Trim().ToLowerInvariant();
+        return Themes.FirstOrDefault(t => t.Id == key) ?? Themes[0];
+    }
+
+    public static bool Exists(string? id)
+    {
+        var key = (id ?? string.Empty).Trim().ToLowerInvariant();
+        return Themes.Any(t => t.Id == key);
+    }
+}