feat: poker session history — browse, delete, and Lyra lookup

Answers three gaps: no way to delete a single poker session (only clear_all),
no way to browse past sessions, and Lyra could only see aggregate stats.

- poker.list_sessions() (per-session summary + hand count + recap flag) and
  poker.delete_session() (removes a session + its hands/reads/observations/
  stacks/rituals; keeps the persistent villain file).
- /history page (date, stakes, venue, net, hours, recap link, per-row delete with
  confirm) + /history/data + DELETE /history/{id}. Nav links from chat + HUD.
- recent_sessions read tool, added to the shared lookups so Lyra can answer
  "how'd my last few sessions go?" in either mode.
- Delete is UI/CLI only — deliberately not a Lyra tool.
- test_modes.py +2 (list/delete, recent_sessions); 44 green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyra/web/static/session.html

@@ -91,6 +91,7 @@
       <span class="dot" id="dot"></span>
       <h1>🎬 Session</h1>
       <a class="back" href="/">← Chat</a>
+      <a class="back" href="/history" title="Past sessions">📚 Sessions</a>
       <a class="back" href="/hands" title="All recorded hands">🃏 Hands</a>
       <span class="updated" id="updated">—</span>
     </div>