Telegram /sessions: paginate the switcher, pin starred, exclude cron

[serxa]

Problem

On Telegram, /sessions surfaced only a handful of recent sessions, and starred (kept-alive) sessions were usually not among them:

• The switcher fetched the 30 most-recently-updated sessions across all sources, then filtered to interactive (telegram/web) ones in Python. Cron/automation sessions update constantly, so they dominated that 30-row window — in practice only a few interactive sessions survived the filter, well under the button cap (a user reported seeing 4).
• Ordering was pure recency, and starring only added a ⭐ to a label if the session already appeared. Since starring exists to keep idle sessions alive, those sessions have an old updated_at and sank below the cutoff — so the sessions a user most wants to return to were the least reachable.
• There was no way to reach anything past the first page.

Change

• New SessionStore.list_interactive_sessions(limit, offset, sources, current_id) that does the work in SQL: filters to interactive sources and non-empty sessions (so cron/automation and 0-message sessions never consume the window), and orders current → starred → most-recent. Exposed through SessionManager and the channel Router.
• _sessions_view_for now fetches one page (page_size + 1, to detect a further page) instead of over-fetching and counting messages per session in Python.
• build_sessions_view renders ⬅️ Prev / ➡️ More buttons (new sess:page:<offset> callback) so every switchable session is reachable. Pinning the current session first keeps it on page 1 regardless of how many starred sessions precede it; starred sessions are pinned ahead of merely-recent ones so an idle kept-alive session is never buried.
• Page size 8 → 10.
• Dropped the per-row ⭐/☆ toggle: Telegram sizes a row's buttons evenly with no API for a narrow second column, so the toggle took half of every session row. The ⭐ stays as a read-only "kept alive" marker in the switch label; star/unstar via /star · /unstar. Each row is now a single full-width tap-to-switch button.

Tests

• tests/test_list_interactive_sessions.py (new) — current→starred→recent ordering; exclusion of cron / empty / archived; pagination via limit/offset; next-page probe.
• tests/test_telegram_sessions.py — updated the switcher tests for the paged, single-button-per-row view; added first/middle/last-page nav assertions.
• Full suite: 3196 passed, 1 pre-existing unrelated failure (test_xmemory_bridge — an xmemory package version mismatch, independent of this change).