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/Migrations/CvSearchDbContextModelSnapshot.cs

@@ -61,6 +61,9 @@ namespace CvSearch.Data.Migrations
                         .HasMaxLength(128)
                         .HasColumnType("nvarchar(128)");
 
+                    b.Property<bool>("RequireKeywordInAnchor")
+                        .HasColumnType("bit");
+
                     b.Property<string>("SearchUrlTemplate")
                         .IsRequired()
                         .HasMaxLength(1024)
@@ -158,6 +161,9 @@ namespace CvSearch.Data.Migrations
                         .HasColumnType("nvarchar(8)")
                         .HasDefaultValue("en");
 
+                    b.Property<string>("Location")
+                        .HasColumnType("nvarchar(max)");
+
                     b.Property<string>("ProviderConfigJson")
                         .HasColumnType("nvarchar(max)");
 
@@ -216,6 +222,9 @@ namespace CvSearch.Data.Migrations
                         .HasColumnType("nvarchar(8)")
                         .HasDefaultValue("en");
 
+                    b.Property<string>("Location")
+                        .HasColumnType("nvarchar(max)");
+
                     b.Property<bool>("Used")
                         .ValueGeneratedOnAdd()
                         .HasColumnType("bit")