chore(release): development & release protocol, PR-time CI, release workflow, distribution rename

[geng-haoran]

• RELEASING.md / CONTRIBUTING.md: branches, PR gates, SemVer, release checklist, cross-repo order
  (MetaSim first, RoboVerse pins a tag), PyPI trusted publishing, branch-protection settings.
• .github/workflows: ci.yml (ruff at the pre-commit pin + -k general on 3.10/3.11 on every PR —
  until now nothing ran on PRs, only the EC2 merge-queue job), pr-title.yml (Conventional Commit
  titles; squash merge uses them), changelog.yml (an [Unreleased] line is required when metasim/
  changes, unless labelled no-changelog), release.yml (tag vX.Y.Z → version check, build, twine
  check, GitHub Release with the CHANGELOG section, PyPI via trusted publishing once the pypi
  environment exists). CODEOWNERS.
• pyproject: distribution renamed to roboverse-metasim — metasim on PyPI belongs to an
  unrelated project, so the current name could never be published. Import name unchanged.
  metasim.__version__ is read from package metadata (single source: pyproject).

Merge order: this PR, then RoboVerse's protocol PR (it renames its dependency to
roboverse-metasim @ git+...; with the old name pip refuses the renamed distribution).

Co-Authored-By: Claude Fable 5.1 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_017i6VtKoovBNed815mWFqxw

🤖 Generated with Claude Code

https://claude.ai/code/session_017i6VtKoovBNed815mWFqxw

[geng-haoran]

Stacked on #26 (base = maint/lint-and-format): the new lint job flagged the pre-existing ruff debt on main that #26 clears, while general (3.10) / general (3.11) were already green. GitHub retargets this PR to main automatically once #26 merges. Merge order: #26 → this → RoboVerse #806 (dependency rename).