feat: multi-Oracle server support with runtime switching

Complete implementation of multi-server Oracle database support:

Backend:
- Multi-pool Oracle with lazy loading per server
- Email-to-server cache for automatic server discovery
- JWT tokens include server_id claim
- /auth/check-identity and /auth/check-email endpoints
- /auth/my-servers endpoint for listing user's accessible servers
- Server switch with password re-authentication

Frontend:
- New ServerSelector component for header dropdown
- Multi-step login flow (identity → server → password)
- Server switching from header with password modal
- Mobile drawer menu with server selection
- Dark mode support for all new components
- URL bookmark support with ?server= query param

Scripts:
- Unified start.sh replacing start-prod.sh/start-test.sh
- Unified ssh-tunnel.sh with multi-server support
- Updated status.sh for new architecture

Tests:
- E2E tests for multi-server and single-server login flows
- Backend unit tests for all new endpoints
- Oracle multi-pool integration tests

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/shared/styles/login.css

@@ -89,8 +89,23 @@
 .login-footer {
   text-align: center;
   padding: 1rem 2rem;
-  background-color: var(--surface-50);
-  border-top: 1px solid var(--surface-200);
+  background-color: var(--surface-ground);
+  border-top: 1px solid var(--surface-border);
+}
+
+.login-footer small {
+  color: var(--text-color-secondary);
+}
+
+/* Dark mode support */
+[data-theme="dark"] .login-footer {
+  background-color: var(--surface-ground);
+}
+
+[data-theme="dark"] .login-error-message {
+  background-color: rgba(239, 68, 68, 0.15);
+  color: var(--red-300);
+  border-color: var(--red-800);
 }
 
 /* Responsive design */