Address review findings on the title-clamp: TITLE_MAX_LEN now reads the length straight
from Notification.title so the clamp can't drift from the column a migration would change
(single source of truth). Add a db-lane test that actually commits a >255-char title into
Postgres (end-to-end proof the truncation is gone, not just the clamp logic) and one that
asserts the constant tracks the column width.
A downloaded FB/IG reel's "title" is the whole caption (up to ~1900 chars). It flowed
untrimmed into Notification.title (String(255)); at the batched download_gc commit that
raised psycopg StringDataRightTruncation in pass 1, aborting the whole run so expiry
deletion, LRU eviction and orphan reap never executed (13/110 prod assets already exceed
the limit). Clamp the title to 255 (with an ellipsis) centrally in create_notification —
defending all six callers — since the full title already reaches the client via `data`
and the column is only an English fallback. Add a regression test.
peter