Fix Cypress: disable allowCypressEnv, hardcode test token, fix CI server wait

- cypress.config.js: set allowCypressEnv: false
- Replace Cypress.env('ADMIN_TOKEN') with hardcoded test DB token
- CI: use fixed venv path, retry loop for server readiness

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

frontend/cypress.config.js

@@ -9,5 +9,6 @@ export default defineConfig({
     viewportHeight: 800,
     video: true,
     videoCompression: false,
+    allowCypressEnv: false,
   },
 })