feat: in-app live log (SSE activity feed)

Turn the inert "Show Work" thinking panel into a real live activity log:
- lyra/logbus.py: thread-safe in-memory ring buffer other modules publish to
- chat.respond logs backend/model/embed per turn, recall counts, reply size;
  web layer logs chat errors
- server: replace the keep-alive /stream/thinking stub with /stream/logs, an
  SSE endpoint that replays the recent buffer then streams new events
- UI: repurpose the panel as a global "Live Log" — connects on load, renders
  level/time/msg/fields, drops the old per-session localStorage + dead popup

Every turn now shows its backend + model in-app, so local-vs-cloud (free vs
paid) is visible at a glance.

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

lyra/web/static/style.css

@@ -907,3 +907,37 @@ select:hover {
     display: none !important;
   }
 }
+
+/* ---- Live Log lines ---- */
+.log-line {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: baseline;
+  gap: 8px;
+  padding: 4px 8px;
+  border-radius: 4px;
+  font-size: 0.8rem;
+  font-family: 'Courier New', monospace;
+  border-left: 3px solid var(--text-fade);
+  animation: thinkingSlideIn 0.25s ease-out;
+  word-break: break-word;
+}
+.log-time { color: var(--text-fade); flex-shrink: 0; }
+.log-level {
+  flex-shrink: 0;
+  text-transform: uppercase;
+  font-size: 0.7rem;
+  font-weight: bold;
+  letter-spacing: 0.05em;
+}
+.log-msg { color: var(--text); }
+.log-fields { color: var(--text-fade); width: 100%; padding-left: 4px; }
+
+.log-info    { border-left-color: #00bfff; }
+.log-info .log-level { color: #7dd3fc; }
+.log-debug   { border-left-color: #8a2be2; }
+.log-debug .log-level { color: #c79cff; }
+.log-error   { border-left-color: #ff3333; background: rgba(255,51,51,0.08); }
+.log-error .log-level, .log-error .log-msg { color: #fca5a5; }
+.log-system  { border-left-color: #00ff66; }
+.log-system .log-level { color: #00ff66; }