Contract + hub: the overview's reports include the ticker's merge items (§6.11, §17)

tsk-f5fw4f4y3pqj open

Gap. The root context entry context/projects.md f55d74ac-1758-4318-8d81-e28dee965939 ("The project overview reuses the project and member reads…") recorded the direction for the moment the hub serves the change ticker's merge items (§17): those merge items are then added to the overview's reports, de-duplicated by pull request number, and do not replace the card reports. The hub serves the merge items now (hub/src/maity_hub/routes/ticker.py, §17.4/§17.9). But GET …/overview (hub/src/maity_hub/routes/overview.py:139) still builds reports from the cards' latest reports alone (latest_reports, :87). docs/api.md §6.11 still says "A merge is a report with pr_state: merged".

Done when:

§6.11 describes the merge items in reports: their shape beside a card report, the de-duplication by pull request number (a merge that a card report already names appears once), and which ticker items a reader sees (the ticker's own audience rules, §17.3/§17.5). The contract change comes first, in its own PR or the same one.
overview.py adds them to reports, newest first, with the same limit, and the card reports stay as they are.
A test in hub/tests/test_overview.py that fails on today's main: a project with the ticker on, one merge the probe observed that no card reports, and one merge a card report names. The overview's reports holds both pull requests, each once.
The KTW entry f55d74ac gets a Verification line in the same PR. Its Revisit "the ticker's merge items are added to reports" (in #1313) then fires.