feat: implement --read-only mode with tool filtering

- Adds --read-only CLI flag to restrict OAuth scopes to read-only permissions
- Implements dynamic tool filtering to disable tools requiring write permissions when in read-only mode
- Updates auth/scopes.py to manage read-only scope mappings
- Enhances @require_google_service and handle_http_errors decorators to propagate scope metadata
- Updates documentation in README.md

README.md

@@ -522,6 +522,13 @@ uv run main.py --tools sheets docs
 uv run main.py --single-user --tools gmail
 ```
 
+
+**🔒 Read-Only Mode**
+```bash
+# Requests only read-only scopes & disables write tools
+uv run main.py --read-only
+```
+
 **★ Tool Tiers**
 ```bash
 uv run main.py --tool-tier core      # ● Essential tools only