docs(contributing): add Git branch discipline rules to copilot instructions

Author: Vineeth Wilson

.github/copilot-instructions.md

@@ -61,6 +61,32 @@ python -m cli chat
 
 Run tests: `pytest tests/unit/` (unit, no Docker) · `pytest tests/integration/` (needs Docker)
 
+## Git Workflow — Branch Discipline
+
+**`master` is protected. Every change — no matter how small — must go through a PR.**
+
+### Rules for all commits (AI agent and human alike)
+1. **Always create a feature branch first** before making any file edits or commits:
+   ```bash
+   git checkout master && git pull
+   git checkout -b <type>/<short-description>
+   ```
+2. **Never commit directly to `master`**. Pushing to `master` is blocked by branch protection and will be rejected.
+3. **Before committing**, verify the active branch is not `master`:
+   ```bash
+   git branch --show-current   # must NOT print "master"
+   ```
+4. **Branch naming convention**: `<type>/<short-description>`
+   - `feat/` — new feature
+   - `fix/` — bug or CI fix
+   - `chore/` — housekeeping (deps, config, docs)
+   - `test/` — adding or fixing tests
+5. **One logical change per PR** — keep diffs focused and reviewable.
+6. After a PR is merged, **always sync local master** before starting the next branch:
+   ```bash
+   git checkout master && git reset --hard origin/master
+   ```
+
 ## Module Conventions
 
 ### `core/config.py`