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/icons.ts

@@ -23,6 +23,7 @@ import {
   mynaLogout,
   mynaPlus,
   mynaRefresh,
+  mynaSearch,
   mynaServers,
   mynaSpinner,
   mynaTrash,
@@ -52,6 +53,7 @@ export const APP_ICONS = {
   mynaLogout,
   mynaPlus,
   mynaRefresh,
+  mynaSearch,
   mynaServers,
   mynaSpinner,
   mynaTrash,