fix(security): owner auth gate, OAuth state cookie binding, 0600 token perms

- Add OWNER_SECRET-based session: signed HMAC cookie, /api/auth/owner login,
  requireOwner middleware. All Tesla routes refuse 401 without it.
- Bind OAuth state to a SameSite=Lax httpOnly cookie at /start, validate
  match in /callback with constant-time compare. Refuses unmatched callbacks.
- Token store now mkdir 0700, writeFile + rename atomic, mode 0600 with
  defensive chmod. Owner-only on disk.
- VIN masked to last 4 in responses; partner-register no longer echoes raw
  Tesla body to clients; coord bounds checked on send-to-nav.
- Client: useTesla also tracks owner status; Connect Tesla button opens an
  OwnerLoginModal when not authenticated, then continues to Tesla OAuth.

Conscious deferrals:
- Explicit CSRF tokens on POST routes: mitigated by SameSite=Lax cookies
  + same-origin CORS. Will revisit if cross-origin clients land.
- At-rest token encryption: deferred for single-user app; tokens are on a
  0700 Dokku volume readable only by the app uid. Will add AES-GCM if we
  multi-tenant.

server/config/env.ts

@@ -25,6 +25,10 @@ export const env = {
   grokEnabled: process.env.GROK_ENABLED !== 'false',
   forceXaiApi: process.env.FORCE_XAI_API === 'true',
 
+  // Owner auth — single-user gate for the Tesla integration until
+  // auth.tony.codes is wired in. Set OWNER_SECRET to a long random string.
+  ownerSecret: process.env.OWNER_SECRET || '',
+
   // Tesla Fleet API
   tesla: {
     // Public key served at /.well-known/appspecific/com.tesla.3p.public-key.pem