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.

JobTrackerApi/Program.cs

@@ -37,6 +37,7 @@ builder.Services.AddSingleton<ICvProcessingQueue, CvProcessingQueue>();
 builder.Services.AddTransient<ProfileCvController>();
 builder.Services.AddSingleton<ICvTemplateRenderer, CvTemplateRenderer>();
 builder.Services.AddSingleton<ICvPdfExporter, PlaywrightCvPdfExporter>();
+builder.Services.AddScoped<ICareerProfileService, CareerProfileService>();
 
 builder.Services.AddSingleton<AppPaths>();
 builder.Services.AddSingleton<IStartupReadiness, StartupReadiness>();