feat: add Terminal Dashboard components and state management

- Implement TerminalTabBar for session tab management with status indicators and alert badges.
- Create TerminalWorkbench to combine TerminalTabBar and TerminalInstance for terminal session display.
- Add localization support for terminal dashboard in English and Chinese.
- Develop TerminalDashboardPage for the main layout of the terminal dashboard with a three-column structure.
- Introduce Zustand stores for session management and issue/queue integration, handling session groups, terminal metadata, and alert management.
- Create a monitor web worker for off-main-thread output analysis, detecting errors and stalls in terminal sessions.
- Define TypeScript types for terminal dashboard state management and integration.

ccw/frontend/src/workers/monitor.worker.ts

@@ -0,0 +1,154 @@
+// ========================================
+// Monitor Web Worker
+// ========================================
+// Off-main-thread rule-based output analysis for terminal sessions.
+// MVP rules:
+//   1. Keyword matching: /error|failed|exception/i -> critical alert
+//   2. Stall detection: no output for > 60s -> warning alert
+//
+// Message protocol:
+//   IN:  { type: 'output', sessionId: string, text: string }
+//   IN:  { type: 'reset', sessionId: string }         -- reset session tracking
+//   OUT: { type: 'alert', sessionId: string, severity: string, message: string }
+
+// ========== Types ==========
+
+interface OutputMessage {
+  type: 'output';
+  sessionId: string;
+  text: string;
+}
+
+interface ResetMessage {
+  type: 'reset';
+  sessionId: string;
+}
+
+type IncomingMessage = OutputMessage | ResetMessage;
+
+interface AlertMessage {
+  type: 'alert';
+  sessionId: string;
+  severity: 'critical' | 'warning';
+  message: string;
+}
+
+interface KeywordRule {
+  pattern: RegExp;
+  severity: 'critical' | 'warning';
+  label: string;
+}
+
+interface SessionState {
+  lastActivity: number;
+  alertCount: number;
+  /** Track stall alert to avoid repeated notifications per stall period */
+  stallAlerted: boolean;
+}
+
+// ========== Rules ==========
+
+const KEYWORD_RULES: KeywordRule[] = [
+  {
+    pattern: /error|failed|exception/i,
+    severity: 'critical',
+    label: 'error keyword',
+  },
+];
+
+/** Stall threshold in milliseconds (60 seconds) */
+const STALL_THRESHOLD_MS = 60_000;
+
+/** Stall check interval in milliseconds (15 seconds) */
+const STALL_CHECK_INTERVAL_MS = 15_000;
+
+// ========== State ==========
+
+const sessions = new Map<string, SessionState>();
+
+// ========== Helpers ==========
+
+function getOrCreateSession(sessionId: string): SessionState {
+  let state = sessions.get(sessionId);
+  if (!state) {
+    state = {
+      lastActivity: Date.now(),
+      alertCount: 0,
+      stallAlerted: false,
+    };
+    sessions.set(sessionId, state);
+  }
+  return state;
+}
+
+function postAlert(alert: AlertMessage): void {
+  self.postMessage(alert);
+}
+
+// ========== Output Processing ==========
+
+function processOutput(sessionId: string, text: string): void {
+  const state = getOrCreateSession(sessionId);
+  state.lastActivity = Date.now();
+  // Reset stall alert flag on new output
+  state.stallAlerted = false;
+
+  // Run keyword rules against text
+  for (const rule of KEYWORD_RULES) {
+    if (rule.pattern.test(text)) {
+      state.alertCount++;
+      postAlert({
+        type: 'alert',
+        sessionId,
+        severity: rule.severity,
+        message: `Detected ${rule.label} in output`,
+      });
+      // Only report first matching rule per chunk to avoid alert flood
+      break;
+    }
+  }
+}
+
+// ========== Stall Detection ==========
+
+function checkStalls(): void {
+  const now = Date.now();
+  sessions.forEach((state, sessionId) => {
+    if (state.stallAlerted) return;
+    const elapsed = now - state.lastActivity;
+    if (elapsed > STALL_THRESHOLD_MS) {
+      state.stallAlerted = true;
+      state.alertCount++;
+      const seconds = Math.floor(elapsed / 1000);
+      postAlert({
+        type: 'alert',
+        sessionId,
+        severity: 'warning',
+        message: `Session stalled: no output for ${seconds}s`,
+      });
+    }
+  });
+}
+
+// ========== Message Handler ==========
+
+self.onmessage = (event: MessageEvent<IncomingMessage>) => {
+  const msg = event.data;
+  switch (msg.type) {
+    case 'output':
+      processOutput(msg.sessionId, msg.text);
+      break;
+    case 'reset':
+      sessions.delete(msg.sessionId);
+      break;
+  }
+};
+
+// ========== Periodic Stall Check ==========
+
+const _stallInterval = setInterval(checkStalls, STALL_CHECK_INTERVAL_MS);
+
+// Cleanup on worker termination (best-effort)
+self.addEventListener('close', () => {
+  clearInterval(_stallInterval);
+});