fix bib/sync.py: use ISO 8601 date format for Zotero timestamps

_now_iso() produced '2026-02-09 18:13:55' but Zotero requires
'2026-02-09T18:13:55Z'. Fixed 9071 dateAdded/dateModified and
345 accessDate values in the live database.

src/bib/sync.py

@@ -72,7 +72,7 @@ def _zotero_key() -> str:
 
 
 def _now_iso() -> str:
-    return datetime.now(timezone.utc).strftime("%Y-%m-%d %H:%M:%S")
+    return datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
 
 
 def _ensure_value(con: sqlite3.Connection, value: str) -> int:

tests/bib/test_sync.py

@@ -106,8 +106,9 @@ class TestZoteroKey:
 class TestNowIso:
     def test_format(self) -> None:
         result = _now_iso()
-        assert len(result) == 19  # "YYYY-MM-DD HH:MM:SS"
-        assert " " in result
+        assert len(result) == 20  # "YYYY-MM-DDTHH:MM:SSZ"
+        assert "T" in result
+        assert result.endswith("Z")
 
 
 # ── _ensure_value ───────────────────────────────────────────────────