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>

Directory.Packages.props

@@ -32,6 +32,8 @@
     <PackageVersion Include="Yarp.ReverseProxy" Version="2.3.0" />
     <PackageVersion Include="MailKit" Version="4.16.0" />
     <PackageVersion Include="PdfPig" Version="0.1.14" />
+    <!-- Browser automation -->
+    <PackageVersion Include="Microsoft.Playwright" Version="1.60.0" />
     <!-- Tooling -->
     <PackageVersion Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" Version="1.23.0" />
   </ItemGroup>