Phase 2: Chat History for Agent Tab

Backend: _get_chat_history() reads JSONL sessions. API: GET /api/agents/{id}/chat-history. Frontend: Chat History tab shows session list with title, model, message count. Click to open session in chat panel.

static/style.css

@@ -1630,3 +1630,41 @@ body.resizing{user-select:none;cursor:col-resize;}
 .error-event-row:hover {
   background: rgba(244, 67, 54, 0.1);
 }
+
+.chat-history-list {
+  padding: 8px;
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+
+.chat-history-row {
+  padding: 10px 12px;
+  border-radius: 8px;
+  background: var(--card-bg);
+  border: 1px solid var(--border);
+  cursor: pointer;
+  transition: background 0.15s;
+}
+
+.chat-history-row:hover {
+  background: var(--row-hover);
+  border-color: var(--accent);
+}
+
+.chat-history-title {
+  font-size: 12px;
+  font-weight: 500;
+  color: var(--text);
+  margin-bottom: 4px;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.chat-history-meta {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  flex-wrap: wrap;
+}