feat: stack quick-capture box on chat page (no LLM)

Slim numeric input below the message box; posts to /session/stack and
drops a confirmation line into the Live Log without a chat turn.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G796GsLCvJQKVN7hwV2cDx

lyra/web/static/style.css

@@ -1231,3 +1231,31 @@ select:hover {
     scroll-behavior: auto !important;
   }
 }
+
+/* Stack quick-capture (2nd input box on the chat page) — logs without the LLM. */
+#stackQuick {
+  display: flex;
+  gap: 8px;
+  align-items: center;
+  padding: 6px 12px;
+  border-top: 1px solid var(--border);
+  background: var(--bg-panel);
+}
+#stackQuick input {
+  flex: 1;
+  min-width: 0;
+  padding: 8px 10px;
+  background: var(--bg-elev);
+  color: inherit;
+  border: 1px solid var(--border);
+  border-radius: 8px;
+}
+#stackQuick button {
+  padding: 8px 14px;
+  background: var(--accent);
+  color: #000;
+  border: none;
+  border-radius: 8px;
+  font-weight: 600;
+  cursor: pointer;
+}