Menu icons, File Locks viewer, remove dock drag highlight

- Add icons to every dropdown menu item (File/Connection/Actions/Window/Tools/Help)
- New File Locks viewer (Window -> File Locks): all open/locked files across the
  depot with who holds them (user + workspace), filter, locked-only toggle,
  unlock your own locks, refresh
- Remove the purple highlight on the bottom-dock resize handle (cursor only)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/Cargo.lock

@@ -960,7 +960,7 @@ dependencies = [
 
 [[package]]
 name = "exbyte-depot"
-version = "0.2.3"
+version = "0.2.4"
 dependencies = [
  "encoding_rs",
  "serde",