fix(browser): stability enhancements + MCP frontend client

S7 Browser Hand:
- Remove dead code: browser/actions.rs (314 lines of unused BrowserAction/ActionResult types)
- Fix browser_scrape_page: log failed selector matches instead of silently swallowing errors
- Fix element_to_info: document known limitation for always-None location/size fields
- Fix browserHandStore: reuse activeSessionId in executeScript/takeScreenshot/executeTemplate
  instead of creating orphan Browser sessions
- Add Browser.connect(sessionId) method for session reuse

MCP Frontend:
- Add desktop/src/lib/mcp-client.ts (77 lines) — typed client for MCP Tauri commands
  (startMcpService, stopMcpService, listMcpServices, callMcpTool)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src-tauri/src/browser/commands.rs

@@ -1,9 +1,5 @@
 // Tauri commands for browser automation
-// Note: Some imports are reserved for future Browser Hand features
 
-#![allow(unused_imports)]
-
-use crate::browser::actions::BrowserAction;
 use crate::browser::client::BrowserClient;
 use crate::browser::session::{BrowserType, SessionConfig};
 use serde::{Deserialize, Serialize};
@@ -454,9 +450,18 @@ pub async fn browser_scrape_page(
     let mut results = serde_json::Map::new();
 
     for selector in selectors {
-        if let Ok(elements) = client.find_elements(&session_id, &selector).await {
-            let texts: Vec<String> = elements.iter().filter_map(|e| e.text.clone()).collect();
-            results.insert(selector, serde_json::json!(texts));
+        match client.find_elements(&session_id, &selector).await {
+            Ok(elements) => {
+                let texts: Vec<String> = elements.iter().filter_map(|e| e.text.clone()).collect();
+                results.insert(selector, serde_json::json!(texts));
+            }
+            Err(e) => {
+                tracing::warn!(
+                    selector = %selector,
+                    error = %e,
+                    "browser_scrape_page: find_elements failed, skipping selector"
+                );
+            }
         }
     }