refactor(db): typed query helpers, shared test FormData helper

Replace raw db.execute tuple casts with queryRows/rowsFrom/execResult/
affectedRows helpers from lib/db, drop redundant mysql2 casts on typed
query builders, and centralize per-test fakeForm into test/fake-form.
Update db mocks in tests so helpers resolve against mocked execute.

src/actions/bulk-users.ts

@@ -23,9 +23,7 @@ export async function bulkUnban({
 }): Promise<ActionResult<{ unbanned: number; total: number }>> {
 	const staff = await requirePermission(PERMS.USERS_EDIT);
 	const result = await db.delete(Ban).where(inArray(Ban.userId, userIds));
-	const unbanned = Number(
-		(result as unknown as [{ affectedRows: number }])[0]?.affectedRows ?? 0,
-	);
+	const unbanned = Number(result[0]?.affectedRows ?? 0);
 	await logStaffActivity({
 		staffId: staff.id,
 		action: "bulk_unban",