Sync main into dev 2026 RC

[leehack]

Summary

• merge main into dev/2026-07-28-rc after the 2.2.1 stable release
• preserve the dev prerelease package version 2.3.0-dev.0 while adding the stable 2.2.1 changelog section to dev history
• carry over the main-branch installer fallback improvements for GitHub API rate-limit resilience
• resolve the overlapping JSON Schema test conflict by retaining the current dev schema coverage

Why

PR #281 tracks merging the 2026 RC dev branch back to main and is currently conflict-blocked. Syncing main into dev first keeps the integration conflict resolution isolated and should make the tracking PR cleaner after this lands.

Validation

• dart format .
• bash -n tool/install.sh
• dart analyze
• dart test
• cd packages/mcp_dart_cli && dart pub get
• cd packages/mcp_dart_cli && dart test test/src/update_command_test.dart

PowerShell is not installed in this environment, so I could not syntax-check tool/install.ps1 locally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.90%. Comparing base (7d2da04) to head (60a8990).
⚠️ Report is 1 commits behind head on dev/2026-07-28-rc.

Additional details and impacted files

@@                  Coverage Diff                  @@
##           dev/2026-07-28-rc     #283      +/-   ##
=====================================================
- Coverage              88.45%   84.90%   -3.55%     
=====================================================
  Files                     48       70      +22     
  Lines                  10728    15383    +4655     
=====================================================
+ Hits                    9489    13061    +3572     
- Misses                  1239     2322    +1083     

Flag	Coverage Δ
cli	76.73% <ø> (?)
unittests	88.45% <ø> (ø)

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