feat(providers): add headless browser scraping via Playwright for SPA job sites

ejobs.ro migrated to a Nuxt SPA - plain HTTP GET returns only the JS
bundle. This change equips cv-search-job with a headless Chromium
(Playwright 1.60) so it can fully render SPA pages before extracting
job links.

- Add UseHeadlessBrowser flag to JobProviderEntity, JobProviderConfig,
  and CvSearchDbContext; map it in JobTokenService.ToConfig so the flag
  is included in the session provider-config snapshot
- Migration: add UseHeadlessBrowser column; fix ejobs.ro search URL
  (remove /user/ prefix that caused 404) and set UseHeadlessBrowser=true
- HtmlJobSearcher: detect flag and dispatch to FetchWithPlaywrightAsync;
  plain-HTTP path is unchanged; NetworkIdle timeout falls back to partial
  content rather than failing outright
- Dockerfile: download Playwright Chromium in the SDK build stage via
  npx; copy browser binaries to the final image; install Chromium system
  libs (Ubuntu noble t64 variants)

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

Apis/cv-search-data/Migrations/CvSearchDbContextModelSnapshot.cs

@@ -66,6 +66,11 @@ namespace CvSearch.Data.Migrations
                         .HasMaxLength(1024)
                         .HasColumnType("nvarchar(1024)");
 
+                    b.Property<bool>("UseHeadlessBrowser")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("bit")
+                        .HasDefaultValue(false);
+
                     b.HasKey("Id");
 
                     b.ToTable("JobProviders", "cvSearch");