perf(zot): create_db runs the schema script as one transaction

executescript autocommitted each of the ~2,500 statements — thousands of
fsyncs — so on a file-backed path under disk load a fresh zotero.sqlite
took 15–20 s. Every prisma test that builds one in tmp_path paid it and
the suite looked hung (my own full run sat 42 min; the #655 agent's runs
never returned). One transaction: 0.02 s, integrity_check ok.

src/zot/schema.py

@@ -32,6 +32,11 @@ def create_db(path: str = ":memory:") -> sqlite3.Connection:
     close it afterward; for ``:memory:`` keep it alive.
     """
     con = sqlite3.connect(path)
-    con.executescript(_load_sql())
+    # One transaction for the whole ~2,500-statement script. executescript
+    # otherwise autocommits every CREATE/INSERT — thousands of fsyncs — and
+    # on a file-backed path under disk load that took 15–20 s per fresh
+    # DB (every prisma test that builds a zotero.sqlite in tmp_path paid
+    # it; the suite looked hung). As one transaction it is ~instant.
+    con.executescript("BEGIN;\n" + _load_sql() + "\nCOMMIT;")
     con.row_factory = sqlite3.Row
     return con