feat: integrate Career Workspace foundation from feature/career-workspace

Recover the F1 Career Profile foundation + AI-workspace persistence from the
unmerged feature/career-workspace branch, so Phase 2 builds on the documented,
tested target state instead of re-deriving it. Foundation only — CV Builder
commits (variants, ATS badge, rewrite diff) stay deferred per "do not build CV
Builder yet". See docs/career-workspace-branch-assessment.md.

Squashed from 3 branch commits (235e291, 5916f09, 00a035e), resolved against
main + Phase 0:

- CareerProfile + CareerProfileVersion (append-only history), dual-written from
  every profile save path via CareerProfileService. ApplicationUser.
  ProfileCvStructureJson stays authoritative; the tables mirror it. Stable item
  IDs assigned to jobs/education/certifications/projects (the prerequisite for
  future variant lineage). CvDateNormalizer for free-text -> YYYY-MM.
- InterviewPrepNote + AiWorkspaceNote: cache AI interview prep / candidate fit /
  focus plan keyed by an attachment-context signature, so they stop regenerating
  (and re-spending the provider) on every open.

Conflict resolutions (union, favouring current code + Phase 0):
- JobTrackerContext / StartupInitializationExtensions: kept Phase 0's tables and
  reconciler blocks, added the career/interview/ai-note tables (both SQLite and
  MySQL dialects).
- ProfileCvController: dropped the branch's in-file DTO records (main defines them
  in ProfileCvDtos.cs) and the LayoutFamily/AtsRating template fields (deferred
  ATS-badge work), keeping main's 7-arg CvTemplateDescriptor.
- JobApplicationsController: kept the branch's cache-check, restored main's
  AsNoTracking on the read-only user load.

Tables ship empty (verified dev); nothing to migrate.

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

Models/StructuredCvProfile.cs

@@ -49,11 +49,19 @@ public sealed class StructuredCvContact
 
 public sealed class StructuredCvJob
 {
+    // Stable item ID (assigned by CareerProfileService on first save). Required for CV variants
+    // to reference "this job" across profile edits, instead of by array position. Nullable/empty
+    // on freshly-parsed or legacy data until the first save assigns it.
+    public string? Id { get; set; }
     public string? Title { get; set; }
     public string? Company { get; set; }
     public string? Location { get; set; }
     public string? Start { get; set; }
     public string? End { get; set; }
+    // Best-effort "YYYY-MM" normalization of Start/End, computed alongside Id assignment.
+    // Null when Start/End can't be parsed; the free-string fields above remain the display source.
+    public string? StartDate { get; set; }
+    public string? EndDate { get; set; }
     public bool IsCurrent { get; set; }
     public List<string> Bullets { get; set; } = new();
     public List<string> Skills { get; set; } = new();
@@ -61,31 +69,39 @@ public sealed class StructuredCvJob
 
 public sealed class StructuredCvEducation
 {
+    public string? Id { get; set; }
     public string? Qualification { get; set; }
     public string? QualificationLevel { get; set; }
     public string? Institution { get; set; }
     public string? Location { get; set; }
     public string? Start { get; set; }
     public string? End { get; set; }
+    public string? StartDate { get; set; }
+    public string? EndDate { get; set; }
     public List<string> Details { get; set; } = new();
 }
 
 public sealed class StructuredCvCertification
 {
+    public string? Id { get; set; }
     public string? Name { get; set; }
     public string? Issuer { get; set; }
     public string? Location { get; set; }
     public string? Date { get; set; }
+    public string? DateNormalized { get; set; }
     public List<string> Details { get; set; } = new();
 }
 
 public sealed class StructuredCvProject
 {
+    public string? Id { get; set; }
     public string? Name { get; set; }
     public string? Role { get; set; }
     public string? Location { get; set; }
     public string? Start { get; set; }
     public string? End { get; set; }
+    public string? StartDate { get; set; }
+    public string? EndDate { get; set; }
     public List<string> Bullets { get; set; } = new();
     public List<string> Skills { get; set; } = new();
 }