Harden AI generation endpoints to use token-derived user identity

[AJaySi]

Motivation

• Prevent clients from supplying authoritative user_id values to public AI generation and retrieval routes.
• Ensure all user identity is derived from verified token claims (id / clerk_user_id) and surface an authentication error when missing.
• Restrict task/strategy reads and optimizations so only the creating (authenticated) user can access them.

Description

• Added current_user: Dict[str, Any] = Depends(get_current_user) to public AI endpoints and removed client-provided user_id parameters from routes such as generate_comprehensive_strategy, generate_strategy_component, get_strategy_generation_status, generate_comprehensive_strategy_polling, get_strategy_generation_status_by_task, and get_latest_generated_strategy.
• Introduced _get_authenticated_user_id(current_user) helper to consistently extract the authenticated user id (string) from token claims and raise HTTPException(status_code=401) when missing.
• Eliminated fallback/default user_id behavior (e.g. request.get("user_id", 1) and query default user IDs) and ensured downstream calls use the authenticated user_id string; removed an unused Query import.
• Added owner authorization checks for task-status and strategy-optimization flows (returning 403 when the authenticated user does not own the requested task/strategy), and added current_user checks to optimize_existing_strategy.
• Added focused static/source-level tests backend/security_test_ai_generation_endpoints_auth.py that verify route signatures, enforcement of token-derived user_id, task-owner authorization, and the 401 on missing authenticated id.

Testing

• Ran pytest -q backend/security_test_ai_generation_endpoints_auth.py, which executed the new auth-hardening assertions and all tests passed (4 passed).
• Ran python -m compileall backend/api/content_planning/api/content_strategy/endpoints/ai_generation_endpoints.py backend/security_test_ai_generation_endpoints_auth.py to validate modules compile successfully (succeeded).

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Codex Task