feat: provision sites end-to-end from the site config app

[MateoLostanlen]

• Extends the Streamlit site_config app to provision a new site in one click: creates the org, cameras and poses in the alert API (reusing init_script/common.py helpers), then writes $REPO_PATH/host_vars/<site>/.
• vars.yml embeds the returned camera id and pose_ids in config_json, plus static-IP defaults and watchdog_type; vars.vault.yml holds the secrets and is encrypted via ansible-vault using VAULT_PASSWORD_FILE.
• API step is idempotent (reuses cameras/poses by name); inputs are validated and the plaintext vault is removed if encryption fails.
• Adds idempotent API helpers and fixes header type hints / a leaked-password debug print in common.py.