Agenda, month view, session detail

- [ ] Agenda: every upcoming session and game day across all campaigns, with quorum state, intent counts, and jeopardy flags — the console counterpart to `/upcoming`.
- [ ] Month grid with the same data; click through to the session.
- [ ] Session detail: roster with intent and attended, thread link, Discord event link, Google sync state (`calendar_links.synced_at` / `last_error`), actions (open a targeted poll, lock, cancel).

Start at the existing `/upcoming` counterpart and trace how upcoming sessions, campaigns, and calendar sync state are loaded. Map the agenda, month grid, and session-detail requirements to the existing console entry points, including the listed roster, links, sync fields, and actions. Done means all three views expose the requested data and the poll, lock, and cancel actions work.

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