Add optional pre-commit hook for code formatting

[jamescrosswell]

Summary

Adds an optional pre-commit git hook that auto-fixes code formatting before allowing commits. This helps catch formatting issues early and reduces CI failures.

Implementation

New files:

• .githooks/pre-commit: Hook script that runs dotnet format against staged .cs files only

Updated files:

• dev.cs: Adds setup-hooks and remove-hooks commands to opt in/out

Behavior:

1. Developer runs ./dev.cs setup-hooks once to enable the hook
2. On each commit, the pre-commit hook runs
3. If unstaged changes are present → hook skips with a warning (dotnet format operates on the working tree, so partially staged files can't be handled safely)
4. Otherwise, dotnet format runs against staged .cs files only and auto-fixes any formatting issues
5. If fixes were applied → commit fails, developer stages the fixes (git add -u) and commits again
6. Can bypass with git commit --no-verify if needed
7. Run ./dev.cs remove-hooks to opt out

Design decisions:

• Auto-fix: Hook applies formatting fixes rather than just reporting them — developer only needs to git add -u and recommit rather than manually running dotnet format
• Staged files only: Uses --include scoped to staged .cs files so only what's being committed gets formatted
• Skip on unstaged changes: If the working tree isn't clean, the hook exits with a warning rather than risking modification of unstaged hunks in partially staged files
• Native git hooks: No external dependencies (Husky.NET not needed)
• Opt-in via dev.cs: Discoverable through the existing dev CLI rather than a separate shell script

Addresses

Fixes #4980

Next Steps

This PR makes the hook optional. After battle testing for a bit, we could:

• Document in CONTRIBUTING.md
• Add other pre-commit checks (analyzers, etc.)

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.08%. Comparing base (32a55e3) to head (2db003e).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5178      +/-   ##
==========================================
+ Coverage   74.06%   74.08%   +0.02%     
==========================================
  Files         501      506       +5     
  Lines       18113    18247     +134     
  Branches     3521     3564      +43     
==========================================
+ Hits        13415    13519     +104     
- Misses       3838     3858      +20     
- Partials      860      870      +10     

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