Remove frontend regex pre-check that truncated paths containing spaces,
quotes, or Windows drive letters. Backend _detect_file_drop correctly
handles these patterns. This fixes image attachment for common filenames
like "Screenshot 2026-04-29.png".
Add tests:
- test_input_detect_drop_path_with_spaces: attaches image with spaces in name
- test_input_detect_drop_path_with_spaces_and_remainder: remainder handling
Also restored missing in test_rollback_restore_resolves_number_and_file_path.
Scope: tui, vision, tests
cc340c4a4d