feat: add career profile foundation with versioned history

Introduces the Career Workspace's bounded data foundation, additive
and backwards-compatible: ApplicationUser.ProfileCvStructureJson
stays the authoritative column every existing read path uses; the new
CareerProfiles/CareerProfileVersions tables mirror it via
ICareerProfileService so future Career Workspace features (variants,
history UI) have real tables to build on rather than starting a
second migration later.

- CareerProfile: one snapshot row per user (Version, ProfileJson).
- CareerProfileVersion: append-only history, one row per save
  (upload/rebuild/improve/reprocess/parse), so a profile edit is never
  silently lost the way ProfileCvStructureJson overwrites are today.
- Stable item IDs assigned to jobs/education/certifications/projects
  on first save and preserved across later saves -- the prerequisite
  for CV variants to reference "this job" by identity instead of
  array position.
- CvDateNormalizer: best-effort free-string -> "YYYY-MM" parsing for
  job/education/certification/project date ranges, kept alongside
  (never replacing) the original free-string fields.
- Both SQLite (dev) and MySQL/MariaDB (prod) reconciler dialects,
  matching this repo's schema-via-raw-SQL-reconciler convention
  rather than EF migrations.

Job tracking is untouched -- this is entirely within the profile/CV
domain per the Career Workspace product boundary.

Data/JobTrackerContext.cs

@@ -28,6 +28,8 @@ namespace JobTrackerApi.Data
     public DbSet<CvUploadArtifact> CvUploadArtifacts => Set<CvUploadArtifact>();
     public DbSet<CvExtractionRun> CvExtractionRuns => Set<CvExtractionRun>();
     public DbSet<TailoredCvDraft> TailoredCvDrafts => Set<TailoredCvDraft>();
+    public DbSet<CareerProfile> CareerProfiles => Set<CareerProfile>();
+    public DbSet<CareerProfileVersion> CareerProfileVersions => Set<CareerProfileVersion>();
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
@@ -141,6 +143,27 @@ namespace JobTrackerApi.Data
             .WithOne(j => j.TailoredCvDraft)
             .HasForeignKey<TailoredCvDraft>(x => x.JobApplicationId)
             .OnDelete(DeleteBehavior.Cascade);
+
+        // 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);
     }
 }
 }