Type-to-filter in file panels

Typing while the list is focused builds a filter query: a bar appears under
the column headers (search icon, query, live match count, Esc hint, clear
button) and the listing narrows to substring matches — '..' always stays.
Backspace edits the query, Escape clears it, cursor parks on the first match,
arrows/Enter keep working (the list never loses focus), and Space keeps its
select meaning until a query exists. Filter resets on directory change and
survives refresh; operations act only on visible (filtered) selection.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/src/app/file-panel/file-panel.ts

@@ -100,6 +100,17 @@ export class FilePanel {
     return this.panel().selected().has(entry.name);
   }
 
+  clearFilter(): void {
+    this.panel().setFilter('');
+    this.listEl().nativeElement.focus();
+  }
+
+  filterMatches(): number {
+    return this.panel()
+      .sorted()
+      .filter((e) => e.name !== '..').length;
+  }
+
   sortIndicator(key: SortKey): string {
     if (this.panel().sortKey() !== key) return '';
     return this.panel().sortAsc() ? '↑' : '↓';
@@ -151,6 +162,31 @@ export class FilePanel {
       return;
     }
 
+    // type-to-filter: printable characters build the query (Space only once a
+    // query exists — an empty-filter Space keeps its toggle-select meaning)
+    if (
+      key.length === 1 &&
+      !event.metaKey &&
+      !event.ctrlKey &&
+      !event.altKey &&
+      (key !== ' ' || panel.filter() !== '')
+    ) {
+      event.preventDefault();
+      panel.setFilter(panel.filter() + key);
+      this.scrollCursorIntoView();
+      return;
+    }
+    if (key === 'Backspace' && panel.filter() !== '') {
+      event.preventDefault();
+      panel.setFilter(panel.filter().slice(0, -1));
+      return;
+    }
+    if (key === 'Escape' && panel.filter() !== '') {
+      event.preventDefault();
+      panel.setFilter('');
+      return;
+    }
+
     switch (key) {
       case 'ArrowDown':
         panel.moveCursor(1);