fix(kb): coerce sidecar date strings to datetime.date for asyncpg

Sidecar JSON supplies published_at / effective_at as 'YYYY-MM-DD' strings.
asyncpg rejects strings for DATE columns even with '::date' casts in the
SQL, so ingest now parses them via datetime.date.fromisoformat before the
INSERT. Non-string inputs (date, datetime, None, empty) are handled too.

Before: ingest crashed on any sidecar with a date, leaving the source in
failed/ while sidecarless siblings succeeded.

Refs Task Master #2

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/services/kb/ingest.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import datetime as _dt
 import hashlib
 import io
 import logging
@@ -20,6 +21,22 @@ class IngestError(RuntimeError):
     pass
 
 
+def _coerce_date(value) -> _dt.date | None:
+    """Accept date objects, 'YYYY-MM-DD' strings, or None; return date|None."""
+    if value is None or value == "":
+        return None
+    if isinstance(value, _dt.date) and not isinstance(value, _dt.datetime):
+        return value
+    if isinstance(value, _dt.datetime):
+        return value.date()
+    if isinstance(value, str):
+        try:
+            return _dt.date.fromisoformat(value[:10])
+        except ValueError:
+            return None
+    return None
+
+
 def _parse_pdf(data: bytes) -> str:
     parts: list[str] = []
     with fitz.open(stream=data, filetype="pdf") as doc:
@@ -125,10 +142,11 @@ async def ingest_source(
                 INSERT INTO kb_source
                     (kind, title, identifier, published_at, effective_at,
                      source_url, original_path, checksum)
-                VALUES ($1,$2,$3,$4::date,$5::date,$6,$7,$8)
+                VALUES ($1,$2,$3,$4,$5,$6,$7,$8)
                 RETURNING id
                 """,
-                kind, title, identifier, published_at, effective_at,
+                kind, title, identifier,
+                _coerce_date(published_at), _coerce_date(effective_at),
                 source_url, original_path, checksum,
             )
             source_id = row["id"]