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/mod.rs

@@ -7,4 +7,4 @@ pub mod client;
 pub mod commands;
 pub mod error;
 pub mod session;
-pub mod actions;
+// pub mod actions; // Removed: dead code — see actions.rs for details