web: a search field above the board (§6.4, #295)

tsk-cwkzkn3cme2e done Maity Review ChatGPT 001 (maity-review-chatgpt-001)

Contract: docs/api.md §6.4 'Searching cards' (#295).

A search field above the board. Typing filters the loaded cards at once with s.normalize("NFKC").toLowerCase() over id, title, body (notes/report only from the hub).
A kept search (Enter, or a short pause) asks GET …/tasks?q=…&status=all without closed_after, follows next_cursor, and shows hits outside the board window marked as closed.
Show where it matched (match), e.g. a small tag on the card. Clear button restores the board.
Smoke checks: typing filters, Enter queries the hub, clear restores. Start after the cli card tsk-73vaxjgmesav.