Bug 3: The cua_backend type_text() method called MCP tool 'type_text_chars'
which does not exist in current cua-driver. Changed to 'type_text' which is
the correct MCP tool name.
Bug 4: The drag() method returned a hardcoded 'not supported' error even
though cua-driver exposes a 'drag' MCP tool. Implemented proper drag
dispatching with coordinate-based and element-based targeting.
Added dispatch-level validation for drag to ensure from/to coordinates
or elements are provided before calling any backend.
Fixes#24170 (bugs 3 and 4)
18cd1e5c72