feat(api): CUST-WP-0018 — API hardening & code quality

T01: Fix datetime.utcnow() → datetime.now(tz=timezone.utc) in MCP server
T02: Wrap _get/_post/_patch/_delete with try/except; return error dicts
T03: Log warnings when write_log skips missing project path
T04: Add priority + due_date_before filters to GET /tasks/
T05: Add owner + slug filters to GET /workstreams/
T06: Add offset param to GET /progress/ for proper pagination
T07: Low-severity bundle:
  - CORS origins from CORS_ORIGINS env var (TD-017)
  - seed.py upsert domains+topics on re-run (TD-011)
  - normalise filter bar CSS → filter-text-input everywhere (TD-016)
  - add 30.5 avg-days-per-month comment in decisions.md (TD-019)
  - TD-009, TD-018 already resolved by existing code

Closes CUST-WP-0018.

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

api/routers/decisions.py

@@ -1,8 +1,11 @@
+import logging
 import uuid
 from datetime import datetime, timezone
 from pathlib import Path
 
 from fastapi import APIRouter, Depends, HTTPException, status
+
+logger = logging.getLogger(__name__)
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
@@ -171,10 +174,12 @@ async def _write_project_log(
                 break
 
     if not project_path:
+        logger.warning("write_log requested but no project_path found for topic %s", decision.topic_id)
         return
 
     p = Path(project_path)
     if not p.is_dir():
+        logger.warning("write_log requested but project_path does not exist: %s", project_path)
         return
 
     now = datetime.now(tz=timezone.utc)