fix: remove API key from plain-text config file, add workflow permissions

- config.py: stop writing API_KEY to .immich_config.json; direct users
  to .env instead. Resolves CodeQL py/clear-text-storage-sensitive-data.
- test.yml, lint.yml: add permissions: contents: read to satisfy
  actions/missing-workflow-permissions scanner.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/test.yml

@@ -9,6 +9,8 @@ on:
 jobs:
   test:
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
     steps:
       - name: Checkout code
         uses: actions/checkout@v4