fix(ci): set stub ANTHROPIC_API_KEY for e2e job so AI-gated endpoints respond

POST /api/v1/ai-sessions and friends call _require_ai_enabled(), which
returns 503 when no provider key is set. The new prefill-handoff
regression test (e2e/assistant-chat-prefill.spec.ts) drives the
dashboard prefill flow, which has to create a chat session before its
page.route stub on /chat can fire — so without a key, session
creation 503s and the test never sees the task lane.

The Playwright stub intercepts /chat in the browser, so the backend
never actually contacts Anthropic — but the AI-enabled gate still
needs to pass. A stub value is enough.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -161,6 +161,12 @@ jobs:
       PLAYWRIGHT_SECRET_KEY: ci-playwright-secret-key
       PLAYWRIGHT_TEST_EMAIL: teamadmin@resolutionflow.example.com
       PLAYWRIGHT_TEST_PASSWORD: TestPass123!
+      # AI-touching endpoints (POST /ai-sessions, /chat, /respond, etc.) are
+      # gated by `_require_ai_enabled()`, which returns 503 when no provider
+      # key is set. Tests that exercise those flows stub the AI calls in the
+      # browser via `page.route`, so the backend never actually contacts
+      # Anthropic — but the gate still has to pass. A stub value is enough.
+      ANTHROPIC_API_KEY: ci-stub-key-not-used-by-tests
 
     steps:
       - uses: actions/checkout@v4