fix(tui): always call input.detect_drop for reliable image attachment

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

ui-tui/src/app/useSubmission.ts

@@ -126,13 +126,9 @@ export function useSubmission(opts: UseSubmissionOptions) {
         return sys('session not ready yet')
       }
 
-      // Plain prompts are the common path and should not pay an extra RPC
-      // before prompt.submit. File-drop detection still runs for absolute,
-      // tilde, file://, and explicit relative paths.
-      if (!looksLikeSlashCommand(text) && !/(?:^|\s)(?:file:\/\/|~\/|\.?\.\/|\/)[^\s]+/.test(text)) {
-        return startSubmit(text, expand(text), showUserMessage)
-      }
-
+      // Always ask the backend whether this looks like a file drop.
+      // The backend's _detect_file_drop handles paths with spaces, quotes,
+      // Windows drive letters, and escaped characters correctly.
       gw.request<InputDetectDropResponse>('input.detect_drop', { session_id: sid, text })
         .then(r => {
           if (!r?.matched) {