feat: support gateway token auth on first connect + signed device reconnect

[mateu]

Summary

• Supports both gateway auth modes by sending auth.password and auth.token in connect payloads.
• Splits connect flow by state:
  • First connect (no stored token): auth-only connect, no device signature block.
  • Returning device (stored token): signed device payload + stored token for auth.token.
• Updates desktop config resolution to prefer gateway.auth.token, with gateway.auth.password / OPENCLAW_GATEWAY_TOKEN fallback.

Why

Fixes first-connect auth/signature mismatch while preserving signed reconnect behavior.

Tests

• Updated tests/gateway-protocol.test.ts
• Added tests/gateway-context.test.tsx (both connect paths)
• Focused tests passing.

Note

• next-env.d.ts generated-path change is intentionally not part of this PR.