feat(ci): add changelog generation workflow and PR lint gate

[kongche-jbw]

Description

Fix several bugs and inconsistencies in the CI configuration across the changelog
generation workflow and the PR lint gate.

Key fixes:

• cliff.toml was silently producing wrong version headers (e.g. cosh/v1.0.0
  instead of 1.0.0) due to trim_start_matches not handling the monorepo tag
  prefix. Fixed via split(pat="/") | last.
• chore/changelog-* branches created by changelog.yml were being rejected by
  the branch-name job in prelint.yml, breaking the automated CHANGELOG PR flow.
• release/** PRs were not covered by lint at all (missing trigger branch).
• Dead code (isIntegrationToMain && false) was removed and the collaborative-track
  note is now expressed as a plain comment.
• All Chinese UI text in CI scripts has been migrated to English for consistency.

Related Issue

• issues/87
  closes feat(ci): add changelog generation workflow and PR lint gate #87

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional change)
• Performance improvement
• CI/CD or build changes

Scope

• cosh (copilot-shell)
• agent-sec-core
• os-skills
• agentsight
• Multiple / Project-wide

Checklist

• I have read the Contributing Guide
• My code follows the project's code style
• I have added tests that prove my fix is effective or that my feature works
• I have updated the documentation accordingly
• For cosh: Lint passes, type check passes, and tests pass
• For agent-sec-core (Rust): cargo clippy -- -D warnings and cargo fmt --check pass
• For agent-sec-core (Python): Ruff format and pytest pass
• For os-skills: Skill directory structure is valid and shell scripts pass syntax check
• Lock files are up to date (package-lock.json / Cargo.lock)

Testing

CI-only changes. Verified by:

1. Manually tracing branch patterns in prelint.yml against chore/changelog-*, release/*, and standard feature/fix/hotfix branches.
2. Reviewing cliff.toml Tera template output for tags in <scope>/v<x.y.z> format.

Additional Notes

• git-cliff is now pinned to v2.4.0. Update VERSION in changelog.yml intentionally when upgrading.
• The merge:commit label referenced in merge-hint must be created in the GitHub repo's label settings before it can be applied automatically.

[samchu-zsl]

LGTM