feat: apply GitHub repo settings and branch protection

[akiojin]

Summary

Closes #10

• develop.json: Fixed check names to match actual GitHub Actions job names (Rust Format & Lint, Markdown & Commitlint, Rust Tests (required), LSP Tests (required), Verify specs/specs.md is up-to-date)
• Repo settings: Applied allow_auto_merge=true and delete_branch_on_merge=true via gh api
• Branch protection: Applied main (Main PR Policy) and develop (5 CI checks) branch protection rules

Changes

File	Change
.github/config/branch-protection/develop.json	Updated check names to match actual workflow jobs
.github/config/README.md	Added manual apply instructions, check name mapping, verification commands

Verification

```bash
gh api repos/akiojin/unity-cli | jq '{allow_auto_merge, delete_branch_on_merge}'
gh api repos/akiojin/unity-cli/branches/main/protection | jq '.required_status_checks.checks'
gh api repos/akiojin/unity-cli/branches/develop/protection | jq '.required_status_checks.checks'
```

Test plan

• Repo settings verified: allow_auto_merge=true, delete_branch_on_merge=true
• Main branch protection verified: Main PR Policy check required
• Develop branch protection verified: 5 CI checks required

🤖 Generated with Claude Code

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch feature/issue-10

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