feat: deterministic CV-to-job match score endpoint

New JobCvMatchService: a pure, AI-free keyword-coverage scorer that
returns a stable, reproducible 0-100 match score plus matched/missing
keyword lists and per-CV-section coverage. Unlike candidate-fit (AI
narrative), it makes no model calls, so results are instant and
identical for identical inputs - the Jobscan-style differentiator.

- GET /api/jobapplications/{id}/match-score
- keywords = curated SkillTagger tags (high weight) + salient posting
  terms (title terms boosted); word-boundary matching avoids false hits
- section coverage shows where CV evidence is concentrated
- fix(SkillTagger): punctuation-tolerant C#/.NET patterns; the old \b
  boundaries silently missed 'C#,' and '.NET,' everywhere they are used
- 7 unit tests on the pure scorer; full backend suite green (104)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

JobTrackerApi/Program.cs

@@ -157,6 +157,7 @@ builder.Services.AddHttpClient("ai-service", client =>
 
 builder.Services.AddMemoryCache();
 builder.Services.AddSingleton<ISummarizerService, SummarizerService>();
+builder.Services.AddSingleton<IJobCvMatchService, JobCvMatchService>();
 builder.Services.AddSingleton<ICvAiClassifier, CvAiClassifier>();
 builder.Services.AddSingleton<ICvAiNormalizer, CvAiNormalizer>();
 builder.Services.AddSingleton<IGoogleTokenValidator, GoogleTokenValidator>();