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/client.rs

@@ -407,8 +407,15 @@ impl BrowserClient {
         let is_displayed = element.is_displayed().await.unwrap_or(false);
         let is_enabled = element.is_enabled().await.unwrap_or(false);
         let is_selected = element.is_selected().await.unwrap_or(false);
-        // Note: location() and size() may not be available in all fantoccini versions
-        // Using placeholder values if not available
+        // KNOWN LIMITATION: location and size are always None.
+        // The fantoccini Element type does not expose a synchronous bounding-box
+        // helper; retrieving geometry requires a separate execute_script call
+        // (e.g. element.getBoundingClientRect()). Since no current caller relies
+        // on these fields, they are intentionally left as None rather than adding
+        // an extra round-trip. If bounding-box data is needed in the future,
+        // add a dedicated browser_element_rect command that calls
+        // execute_script("return arguments[0].getBoundingClientRect()") and
+        // deprecate the location/size fields on ElementInfo entirely.
         let location = None;
         let size = None;