security: harden dashboard (SSH keys, auth, uploads, CORS, non-root)

Remove SSH private keys from git, add SECRET_KEY validation, move WS
auth from query string to first message, add session limits/idle timeout,
PBKDF2 Fernet key, refresh token rotation, TOTP replay protection,
file upload size limit + filename sanitization, symlink safety check,
restrict CORS methods, IP-gate OpenClaw token, run container as non-root,
rate-limit refresh/passkey endpoints, sanitize Gitea path params.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -4,3 +4,4 @@ dist/
 *.tar.gz
 __pycache__/
 dashboard/nas-dashboard.tar
+dashboard/ssh/