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/secure_storage.rs

@@ -9,6 +9,7 @@ use keyring::Entry;
 const SERVICE_NAME: &str = "zclaw";
 
 /// Store a value securely in the OS keyring
+// @connected
 #[tauri::command]
 pub fn secure_store_set(key: String, value: String) -> Result<(), String> {
     let entry = Entry::new(SERVICE_NAME, &key).map_err(|e| {
@@ -31,6 +32,7 @@ pub fn secure_store_set(key: String, value: String) -> Result<(), String> {
 }
 
 /// Retrieve a value from the OS keyring
+// @connected
 #[tauri::command]
 pub fn secure_store_get(key: String) -> Result<String, String> {
     let entry = Entry::new(SERVICE_NAME, &key).map_err(|e| {
@@ -53,6 +55,7 @@ pub fn secure_store_get(key: String) -> Result<String, String> {
 }
 
 /// Delete a value from the OS keyring
+// @connected
 #[tauri::command]
 pub fn secure_store_delete(key: String) -> Result<(), String> {
     let entry = Entry::new(SERVICE_NAME, &key).map_err(|e| {
@@ -78,6 +81,7 @@ pub fn secure_store_delete(key: String) -> Result<(), String> {
 }
 
 /// Check if secure storage is available on this platform
+// @connected
 #[tauri::command]
 pub fn secure_store_is_available() -> bool {
     // Try to create a test entry to verify keyring is working