fix: use Zotero-valid charset in key generator (no 0, 1, O, L)

_generate_key() used string.ascii_uppercase + string.digits which
includes 0, 1, O, L — all invalid in Zotero's key charset. This
caused newly created items to fail Zotero sync and pincite regex
matching.

Root cause of the rekeying needed for 10,236 items.

src/bib/store.py

@@ -21,7 +21,6 @@ import mimetypes
 import random
 import shutil
 import sqlite3
-import string
 from importlib import resources
 from pathlib import Path
 from typing import Any
@@ -30,8 +29,8 @@ from bib.item import Item
 
 
 def _generate_key() -> str:
-    """8-char alphanumeric key."""
+    """8-char key using Zotero-compatible charset (no 0, 1, O, L)."""
-    chars = string.ascii_uppercase + string.digits
+    chars = "23456789ABCDEFGHIJKLMNPQRSTUVWXYZ"
     return "".join(random.choices(chars, k=8))  # noqa: S311