docs: add git branching strategy and merge workflow to AGENTS.md

- Add branching strategy section with prefix conventions (feat/, fix/, refactor/, docs/, chore/)
- Add completion and merge workflow steps (branch from dev, merge back, push)
- Emphasize no direct commits to main or dev branches

AGENTS.md

@@ -87,6 +87,31 @@ Do not claim completion without verification evidence.
 
 ## Git workflow
 
+### Branching strategy
+
+For every spec change or new functionality:
+
+1. Create a new branch from `dev` with a proper prefix:
+   - `feat/` for new features (e.g., `feat/tool-workshop`)
+   - `fix/` for bug fixes (e.g., `fix/terminal-tty`)
+   - `refactor/` for refactors (e.g., `refactor/api-cleanup`)
+   - `docs/` for documentation (e.g., `docs/api-guide`)
+   - `chore/` for maintenance (e.g., `chore/update-deps`)
+2. Branch name should reference the OpenSpec change name when applicable.
+3. Do not commit directly to `main` or `dev`.
+
+### Completion and merge
+
+When implementation is complete and verified:
+
+1. Ensure all tests pass and quality gates are met.
+2. Stage all changes with `git add -A`.
+3. Create a commit with a proper conventional commit message (see below).
+4. Switch to `dev`: `git checkout dev`.
+5. Merge the feature branch: `git merge --no-ff <branch-name>`.
+6. Push to remote: `git push origin dev`.
+7. Delete the local feature branch if desired: `git branch -d <branch-name>`.
+
 ### Auto-commit on spec completion
 
 When an OpenSpec change is fully implemented and all tasks are complete: