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>

Data/JobTrackerContext.cs

@@ -32,6 +32,10 @@ namespace JobTrackerApi.Data
     public DbSet<TwoFactorRecoveryCode> TwoFactorRecoveryCodes => Set<TwoFactorRecoveryCode>();
     public DbSet<TrustedDevice> TrustedDevices => Set<TrustedDevice>();
     public DbSet<UserSession> UserSessions => Set<UserSession>();
+    public DbSet<CareerProfile> CareerProfiles => Set<CareerProfile>();
+    public DbSet<CareerProfileVersion> CareerProfileVersions => Set<CareerProfileVersion>();
+    public DbSet<InterviewPrepNote> InterviewPrepNotes => Set<InterviewPrepNote>();
+    public DbSet<AiWorkspaceNote> AiWorkspaceNotes => Set<AiWorkspaceNote>();
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
@@ -216,6 +220,57 @@ namespace JobTrackerApi.Data
 
         modelBuilder.Entity<UserSession>()
             .HasIndex(x => x.UserId);
+
+        // Career Workspace foundation (docs/career-workspace-implementation-roadmap.md Phase F1).
+        // One CareerProfile per user for now -- see roadmap "Not now: multiple profiles per user".
+        modelBuilder.Entity<CareerProfile>()
+            .HasQueryFilter(x => CurrentUserId != null && x.OwnerUserId == CurrentUserId);
+
+        modelBuilder.Entity<CareerProfile>()
+            .HasIndex(x => x.OwnerUserId)
+            .IsUnique();
+
+        modelBuilder.Entity<CareerProfileVersion>()
+            .HasQueryFilter(x => CurrentUserId != null && x.OwnerUserId == CurrentUserId);
+
+        modelBuilder.Entity<CareerProfileVersion>()
+            .HasIndex(x => new { x.OwnerUserId, x.CareerProfileId, x.Version });
+
+        modelBuilder.Entity<CareerProfileVersion>()
+            .HasOne(x => x.CareerProfile)
+            .WithMany()
+            .HasForeignKey(x => x.CareerProfileId)
+            .OnDelete(DeleteBehavior.Cascade);
+
+        // Interview prep persistence (career-workspace-implementation-roadmap.md Phase F5).
+        modelBuilder.Entity<InterviewPrepNote>()
+            .HasQueryFilter(x => CurrentUserId != null && x.OwnerUserId == CurrentUserId);
+
+        modelBuilder.Entity<InterviewPrepNote>()
+            .HasIndex(x => new { x.OwnerUserId, x.JobApplicationId })
+            .IsUnique();
+
+        modelBuilder.Entity<InterviewPrepNote>()
+            .HasOne(x => x.JobApplication)
+            .WithMany()
+            .HasForeignKey(x => x.JobApplicationId)
+            .OnDelete(DeleteBehavior.Cascade);
+
+        // Generic AI workspace note persistence (candidate fit, focus plan) -- same rationale as
+        // InterviewPrepNote above, generalized because these DTOs are irregular/nested enough that
+        // per-field columns would be unreasonable.
+        modelBuilder.Entity<AiWorkspaceNote>()
+            .HasQueryFilter(x => CurrentUserId != null && x.OwnerUserId == CurrentUserId);
+
+        modelBuilder.Entity<AiWorkspaceNote>()
+            .HasIndex(x => new { x.OwnerUserId, x.JobApplicationId, x.NoteType })
+            .IsUnique();
+
+        modelBuilder.Entity<AiWorkspaceNote>()
+            .HasOne(x => x.JobApplication)
+            .WithMany()
+            .HasForeignKey(x => x.JobApplicationId)
+            .OnDelete(DeleteBehavior.Cascade);
     }
 }
 }