Fix rendered crawl startup, document capture, and CI fixtures

[PrzemyslawKlys]

Rendered crawls prepare their browser session before the first navigation, so request routes and initialization scripts apply to the destination. Capture HTML, title, URL and document identity together after interactions, and retry a replaced execution context within the existing capture deadline. A committed non-HTTP destination is skipped without carrying over the previous response metadata. Public session navigation and configured form login retain their existing behavior.

The HTTP and browser fixtures now wait for complete request headers and observe when a stalled read has started before testing cancellation. Unknown-length response-limit checks use a generated stream, and the PowerShell fixtures use syntax supported by Windows PowerShell's C# compiler. The script recipe fixture gives its script step the tested 100 ms limit while page navigation uses the normal deadline. This includes the fixture fixes from #494 and #496 so CI can exercise them with the browser correction.

Validation: all 1,573 tests pass in the full .NET 10 suite. The HTTP, structure and split-packet header cases pass on .NET 10, .NET 8 and .NET Framework 4.7.2. All 25 public crawl cases, both public routing/login-isolation cases and three recipe timeout/navigation/error cases pass in PowerShell 5.1 and 7.

[codecov]

Codecov Report

❌ Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 58.08%. Comparing base (0b55f02) to head (bd7bb25).

Files with missing lines	Patch %	Lines
Sources/HtmlTinkerX/HtmlCrawler.Browser.cs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                  Coverage Diff                  @@
##           v2-speedygonzales     #487      +/-   ##
=====================================================
+ Coverage              58.05%   58.08%   +0.03%     
=====================================================
  Files                    486      487       +1     
  Lines                  36054    36021      -33     
  Branches                7249     7252       +3     
=====================================================
- Hits                   20930    20923       -7     
+ Misses                 12757    12734      -23     
+ Partials                2367     2364       -3     

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