docs: add git workflow and auto-commit rules to AGENTS.md

Add section documenting:
- Auto-commit on OpenSpec completion
- Conventional commit format requirements
- Commit scope rules
- Integration with definition of done

AGENTS.md

@@ -85,6 +85,36 @@ Before completion, report:
 
 Do not claim completion without verification evidence.
 
+## Git workflow
+
+### Auto-commit on spec completion
+
+When an OpenSpec change is fully implemented and all tasks are complete:
+
+1. Stage all changes with `git add -A`
+2. Create a commit with a proper conventional commit message
+3. The commit message should:
+   - Use conventional commit format (`feat:`, `fix:`, `refactor:`, etc.)
+   - Reference the OpenSpec change name and relevant user stories
+   - Include a brief summary of what changed
+   - Mention quality gate results (tests passed, etc.)
+   - Example:
+     ```
+     feat: implement user profile management
+     
+     - Add authenticated profile endpoints (GET/PUT /users/me)
+     - Add avatar upload with file validation
+     - Create frontend profile page
+     
+     Quality gates: pytest (50 passed), ruff, mypy
+     ```
+
+### Commit scope
+
+- One commit per completed OpenSpec change (or related group of changes)
+- Do not commit untested or broken code
+- Do not commit secrets, .env files, or credentials
+
 ## Definition of done
 
 A task is done when:
@@ -94,4 +124,5 @@ A task is done when:
 * Relevant tests/checks passed or limitations are stated.
 * No unrelated scope was added.
 * Remaining risks or follow-ups are documented.
+* Changes are committed with a proper conventional commit message.