exclude browser stress tests from default ci

[KSemenenko]

Summary

• tag the hosted-browser 1 GiB Playwright flows as BrowserStress
• exclude BrowserStress from the default build-and-test and Release workflows
• document that BrowserStress remains an explicit local verification lane instead of a default GitHub-hosted runner check

Verification

• dotnet test Tests/ManagedCode.Storage.Tests/ManagedCode.Storage.Tests.csproj --configuration Release --filter "Category!=BrowserStress"
• dotnet format ManagedCode.Storage.slnx
• dotnet build ManagedCode.Storage.slnx

[Copilot]

Pull request overview

This PR reclassifies the hosted-browser 1 GiB Playwright “large flow” integration tests as an explicit stress lane and removes them from the default GitHub Actions CI paths to keep build-and-test/Release runtimes and stability aligned with historical expectations.

Changes:

• Tagged the two hosted-browser 1 GiB Playwright flows with Category=BrowserStress.
• Updated build-and-test and Release workflows to exclude Category=BrowserStress by default.
• Documented how to include/exclude BrowserStress locally and clarified CI intent in docs.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Tests/ManagedCode.Storage.Tests/Storages/Browser/BrowserWasmStorageIntegrationTests.cs	Marks the WASM-hosted 1 GiB flow as BrowserStress for selective execution.
Tests/ManagedCode.Storage.Tests/Storages/Browser/BrowserServerStorageIntegrationTests.cs	Marks the Server-hosted 1 GiB flow as BrowserStress for selective execution.
.github/workflows/ci.yml	Excludes BrowserStress tests from the default CI test run (and coverage collection).
.github/workflows/release.yml	Excludes BrowserStress tests from the Release workflow test run.
docs/Testing/strategy.md	Adds documentation for the BrowserStress category and how to run/skip it.
docs/Development/setup.md	Notes that CI excludes BrowserStress and how to run it explicitly.
AGENTS.md	Records the repo preference to avoid CI runtime regressions from long browser stress lanes.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.55%. Comparing base (710b8bb) to head (89b4865).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #118      +/-   ##
==========================================
- Coverage   57.27%   48.55%   -8.72%     
==========================================
  Files         133      153      +20     
  Lines        6540     7702    +1162     
  Branches      922     1029     +107     
==========================================
- Hits         3746     3740       -6     
- Misses       2362     3528    +1166     
- Partials      432      434       +2     

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