feat: thought loop — Lyra's threaded, surfaceable train of thought

Built from her own 6-19 idea: a continuing train of thought she keeps across
days, organized into threads she returns to, that she can bring TO Brian and
that his feedback advances or closes. Where the dream cycle's reflect() gives
isolated, overwriting reflections, the thought loop adds continuity (threads),
surfacing (#6 — she leads with a thought when Brian returns after a gap), and a
feedback loop (his reply folds in next pass).

- lyra/thoughts.py: thought_threads + thoughts tables; think() with
  new/continue/respond modes; salience-gated maybe_surface(); record_response()
  feedback; lazy-schema _c() mirroring poker.
- dream.py: curiosity stage advances the loop after reflecting (error-isolated).
- chat.py: build_messages surfaces the top thread after a >=90min gap, once.
- web: /thoughts feed (page + data + respond + status routes), thoughts.html,
  nav 💭 entry. lyra-think entry point. Every thought also lands in her journal.
- clock.gap_seconds(); tests/test_thoughts.py (8 tests). Full suite 58 passing.

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

lyra/web/static/nav.js

@@ -8,6 +8,7 @@
     { href: "/history", icon: "📚", label: "History" },
     { href: "/hands",   icon: "🃏", label: "Hands" },
     { href: "/self",    icon: "🧠", label: "Mind" },
+    { href: "/thoughts", icon: "💭", label: "Thoughts" },
     { href: "/journal", icon: "📔", label: "Journal" },
     { href: "/logs",    icon: "📜", label: "Logs" },
   ];