fix(error): add global error handler, fix stores and dispatcher

- Global unhandledrejection handler with IPC+network filtering
- Agent dispatcher heartbeat uses handleInfraError (was fire-and-forget)
- All stores: layout, workspace, anchors, theme, plugins, machines,
  wake-scheduler — silent failures replaced with handleInfraError
- initGlobalErrorHandler() called in App.svelte onMount

src/App.svelte

@@ -18,6 +18,8 @@
     triggerFocusFlash, emitProjectTabSwitch, emitTerminalToggle,
   } from './lib/stores/workspace.svelte';
   import { disableWakeScheduler } from './lib/stores/wake-scheduler.svelte';
+  import { initGlobalErrorHandler } from './lib/utils/global-error-handler';
+  import { handleInfraError } from './lib/utils/handle-error';
   import { pruneSeen } from './lib/adapters/btmsg-bridge';
   import { invoke } from '@tauri-apps/api/core';
 
@@ -94,6 +96,9 @@
   }
 
   onMount(() => {
+    // Global unhandled rejection safety net
+    initGlobalErrorHandler();
+
     // Step 0: Theme
     initTheme();
     getSetting('project_max_aspect').then(v => {
@@ -114,7 +119,7 @@
     // Step 2: Agent dispatcher
     startAgentDispatcher();
     startHealthTick();
-    pruneSeen().catch(() => {}); // housekeeping: remove stale seen_messages on startup
+    pruneSeen().catch(e => handleInfraError(e, 'app.pruneSeen')); // housekeeping: remove stale seen_messages on startup
     markStep(2);
 
     // Disable wake scheduler in test mode to prevent timer interference