refactor(ci): split CI into separate PR and Release workflows

[0Chencc]

Summary

• Replace unified ci.yml with dedicated pr.yml and release.yml
• Add smart path filtering using dorny/paths-filter for PR builds
• Only build affected platforms based on file changes (core/windows/macos/linux/android/ios)
• Skip draft PRs to save CI resources
• Simplify release workflow to trigger directly on tags (no longer depends on workflow_run)

Changes

pr.yml (new)

• Code quality checks always run (format, analyze, test, complexity, security)
• Platform builds only run when affected files change
• Supports workflow_dispatch for manual full platform builds

release.yml (rewritten)

• Triggered directly by v* tags
• Supports manual dispatch with tag input
• Builds all platforms and creates GitHub Release
• No code signing (unsigned builds)

Test plan

• Create a PR that only changes lib/ files → verify all platforms build
• Create a PR that only changes windows/ files → verify only Windows builds
• Push a v* tag → verify release workflow triggers and creates GitHub Release

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.42%. Comparing base (72267e5) to head (88fc4e0).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main       #2   +/-   ##
=======================================
  Coverage   71.42%   71.42%           
=======================================
  Files           1        1           
  Lines           7        7           
=======================================
  Hits            5        5           
  Misses          2        2           

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