Fix job search: location filtering, keyword quality, anchor filter bypass

Closes #41

- Add RequireKeywordInAnchor per-provider flag (default true); set false for
  ejobs.ro and bestjobs.eu so Stage 2 anchor-text filter is skipped — their
  search URL already filters by relevance server-side
- Update AI system prompts (en + ro) to extract concise job-board-friendly
  keywords (role title + key tech, not abstract concepts) and candidate location
- Propagate location through JobMatchResponse -> CreateJobSearchTokenRequest ->
  JobSearchTokenEntity -> JobSearchSessionEntity
- Add {location} and {location-slug} substitution in HtmlJobSearcher
- Update provider SearchUrlTemplates to include location:
    ejobs.ro:    /locuri-de-munca/{location-slug}?q={keywords}
    bestjobs.eu: /ro/locuri-de-munca-in-{location-slug}?keywords={keywords}
    linkedin.com: ?keywords={keywords}&location={location}
- Three new migrations: AddRequireKeywordInAnchorAndLocation,
  ImproveKeywordsAndAddLocation, AddLocationToProviders

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Apis/cv-search-data/Data/Entities/JobProviderEntity.cs

@@ -33,4 +33,10 @@ public sealed class JobProviderEntity
 
     /// <summary>When true, the scraper renders the page with headless Chromium instead of a plain HTTP GET.</summary>
     public bool UseHeadlessBrowser { get; set; }
+
+    /// <summary>
+    /// When false, the Stage 2 anchor-text keyword filter is skipped.
+    /// Set to false for providers whose search URL already filters by relevance server-side (ejobs.ro, bestjobs.eu).
+    /// </summary>
+    public bool RequireKeywordInAnchor { get; set; } = true;
 }