Add CI lint for hardcoded user_id and gate demo-sensitive routers via ALWRITY_DEMO_RELEASE

[AJaySi]

Motivation

• Prevent accidental shipping of forced/hardcoded user IDs (e.g. user_id = 1, force user_id) outside of test fixtures by failing CI checks.
• Ensure demo-only functionality (Facebook/LinkedIn/persona routers) can be safely disabled for demo releases and that disabled routers are absent from the /api/routers/status listing.

Description

• Add a new GitHub Actions workflow .github/workflows/lint-forced-user-id.yml that runs a repository check on PRs and pushes to main to detect forced/hardcoded user_id patterns.
• Add backend/scripts/check_forced_user_id_patterns.py, a script that scans python sources (while excluding tests/fixtures and the script itself) and fails on patterns like \buser_id\s*=\s*1\b and force user_id.
• Implement demo-release gating in RouterManager (backend/alwrity_utils/router_manager.py) via a _demo_release_mode_enabled() helper that reads ALWRITY_DEMO_RELEASE and skips inclusion of facebook_writer, linkedin, linkedin_image, and persona routers when enabled so they do not appear in included_routers.
• Remove hardcoded user-id usage in affected flows by switching persona endpoints to use the authenticated current_user and by replacing other forced user_id occurrences with either request-derived IDs or an environment-configurable fallback (ALWRITY_FALLBACK_USER_ID), and update monitoring/strategy services to resolve user IDs from DB records where appropriate.
• Add a release-readiness assertion in backend/sif_release_readiness_checks.py to check the presence of the demo-release guard strings in the router manager source.

Testing

• Ran the new lint script python backend/scripts/check_forced_user_id_patterns.py which reported no violations after the code updates (passed).
• Ran python -m py_compile against the modified modules to validate syntax (passed).
• Ran the release-readiness unit suite with PYTHONPATH=backend python -m unittest backend/sif_release_readiness_checks.py, which exercises the added source check, but the run reported a pre-existing unrelated test error (ContentGuardianAgent missing verify_originality) that caused the suite to fail and is not caused by these changes.
• The CI workflow is configured to execute the lint check on pull_request and push to main so the repository will block merges that reintroduce forbidden patterns.

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Codex Task