fix: enable private field access in UpdateComponentTool

Use SerializedObject API as primary method for modifying component
fields, with enhanced reflection as fallback. This fixes three issues:

1. Private fields in base classes now accessible (recursive type search)
2. Asset references can be set by path or GUID
3. Nested field paths supported via SerializedObject.FindProperty()

Co-authored-by: Cursor <cursoragent@cursor.com>