docs: add mandatory rules for package management and English-only policy to CLAUDE.md

CLAUDE.md

@@ -9,3 +9,14 @@ Before taking any action or writing code, you MUST read the following Single Sou
 3. `dev_docs/SESSION_STATE.md` (Contains the current handover status from the previous AI).
 
 Do not proceed with any task until you have analyzed these three files.
+
+## Mandatory Rules
+
+1. **Package Management** — MANDATORY
+   - Any new package installed via `pip install` MUST be added to `backend/requirements.txt`
+   - Keep requirements.txt synchronized with actual installed packages
+   - Document version constraints (e.g., `slowapi>=0.1.9`)
+
+2. **English Only** — MANDATORY
+   - All code, comments, docstrings, and commit messages must be in English
+   - Production files (code, docs) are English-only; only user-AI discussion may use Romanian