fix(tauri): replace silent let _ = with structured logging across 20 modules

Replace error-swallowing let _ = patterns with tracing::warn! in browser,
classroom, gateway, intelligence, memory, pipeline, secure_storage, and
viking command handlers. Ensures errors are observable in production logs.

desktop/src-tauri/src/classroom_commands/chat.rs

@@ -47,6 +47,7 @@ pub struct ClassroomChatCmdRequest {
 // ---------------------------------------------------------------------------
 
 /// Send a message in the classroom chat and get multi-agent responses.
+// @connected
 #[tauri::command]
 pub async fn classroom_chat(
     store: State<'_, ClassroomStore>,
@@ -107,6 +108,7 @@ pub async fn classroom_chat(
 }
 
 /// Retrieve chat history for a classroom
+// @connected
 #[tauri::command]
 pub async fn classroom_chat_history(
     chat_store: State<'_, ChatStore>,

desktop/src-tauri/src/classroom_commands/export.rs

@@ -32,6 +32,7 @@ pub struct ClassroomExportResponse {
 // Command
 // ---------------------------------------------------------------------------
 
+// @reserved: 暂无前端集成
 #[tauri::command]
 pub async fn classroom_export(
     store: State<'_, ClassroomStore>,

desktop/src-tauri/src/classroom_commands/generate.rs

@@ -88,6 +88,7 @@ fn stage_name(stage: &GenerationStage) -> &'static str {
 /// Start classroom generation (4-stage pipeline).
 /// Progress events are emitted via `classroom:progress`.
 /// Supports cancellation between stages by removing the task from GenerationTasks.
+// @connected
 #[tauri::command]
 pub async fn classroom_generate(
     app: AppHandle,
@@ -232,6 +233,7 @@ pub async fn classroom_generate(
 }
 
 /// Get current generation progress for a topic
+// @reserved: 暂无前端集成
 #[tauri::command]
 pub async fn classroom_generation_progress(
     tasks: State<'_, GenerationTasks>,
@@ -248,6 +250,7 @@ pub async fn classroom_generation_progress(
 }
 
 /// Cancel an active generation
+// @connected
 #[tauri::command]
 pub async fn classroom_cancel_generation(
     tasks: State<'_, GenerationTasks>,
@@ -259,6 +262,7 @@ pub async fn classroom_cancel_generation(
 }
 
 /// Retrieve a generated classroom by ID
+// @connected
 #[tauri::command]
 pub async fn classroom_get(
     store: State<'_, ClassroomStore>,
@@ -271,6 +275,7 @@ pub async fn classroom_get(
 }
 
 /// List all generated classrooms (id + title only)
+// @reserved: 暂无前端集成
 #[tauri::command]
 pub async fn classroom_list(
     store: State<'_, ClassroomStore>,