refactor(desktop): ChatStore structured split + IDB persistence + stream cancel

Split monolithic chatStore.ts (908 lines) into 4 focused stores:
- chatStore.ts: facade layer, owns messages[], backward-compatible selectors
- conversationStore.ts: conversation CRUD, agent switching, IndexedDB persistence
- streamStore.ts: streaming orchestration, chat mode, suggestions
- messageStore.ts: token tracking

Key fixes from 3-round deep audit:
- C1: Fix Rust serde camelCase vs TS snake_case mismatch (toolStart/toolEnd/iterationStart)
- C2: Fix IDB async rehydration race with persist.hasHydrated() subscribe
- C3: Add sessionKey to partialize to survive page refresh
- H3: Fix IDB migration retry on failure (don't set migrated=true in catch)
- M3: Fix ToolCallStep deduplication (toolStart creates, toolEnd updates)
- M-NEW-2: Clear sessionKey on cancelStream

Also adds:
- Rust backend stream cancellation via AtomicBool + cancel_stream command
- IndexedDB storage adapter with one-time localStorage migration
- HMR cleanup for cross-store subscriptions

desktop/src-tauri/src/kernel_commands/trigger.rs

@@ -96,6 +96,7 @@ impl From<zclaw_kernel::trigger_manager::TriggerEntry> for TriggerResponse {
 }
 
 /// List all triggers
+// @connected
 #[tauri::command]
 pub async fn trigger_list(
     state: State<'_, KernelState>,
@@ -109,6 +110,7 @@ pub async fn trigger_list(
 }
 
 /// Get a specific trigger
+// @connected
 #[tauri::command]
 pub async fn trigger_get(
     state: State<'_, KernelState>,
@@ -125,6 +127,7 @@ pub async fn trigger_get(
 }
 
 /// Create a new trigger
+// @connected
 #[tauri::command]
 pub async fn trigger_create(
     state: State<'_, KernelState>,
@@ -179,6 +182,7 @@ pub async fn trigger_create(
 }
 
 /// Update a trigger
+// @connected
 #[tauri::command]
 pub async fn trigger_update(
     state: State<'_, KernelState>,
@@ -205,6 +209,7 @@ pub async fn trigger_update(
 }
 
 /// Delete a trigger
+// @connected
 #[tauri::command]
 pub async fn trigger_delete(
     state: State<'_, KernelState>,
@@ -222,6 +227,7 @@ pub async fn trigger_delete(
 }
 
 /// Execute a trigger manually
+// @reserved: 暂无前端集成
 #[tauri::command]
 pub async fn trigger_execute(
     state: State<'_, KernelState>,