docs: update README and CLAUDE.md for install script and backup

- README: add Setup/Install section (install.py), Development Workflow
  (dev-restart.sh), and Backup (restic/backup.sh) sections; fix
  .env.example reference → .env.default
- CLAUDE.md: replace stale Docker start command with install.py

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -98,8 +98,8 @@ Cortex_and_Inara_dev/
 ## Run Commands
 
 ```bash
-# Start (Docker)
-docker compose up -d
+# First-time setup or update on any machine
+python3 install.py
 
 # Restart service (after any Python change)
 systemctl --user restart cortex