Include project rules in commit message generation (#44921)

Closes #38027

Release Notes:

- AI-generated commit messages now respect rules files (e.g.
`AGENTS.md`) if present

---------

Co-authored-by: Claude Haiku 4.5 <noreply@anthropic.com>

Cargo.lock

@@ -7077,6 +7077,7 @@ dependencies = [
  "picker",
  "pretty_assertions",
  "project",
+ "prompt_store",
  "rand 0.9.2",
  "recent_projects",
  "remote",