ui: edit/delete buttons for custom files

- each row now shows Edit and Delete buttons (same styling as the
  profiler list buttons) instead of the red X glyph
- Edit reloads the entry into the top form: the Add button becomes
  Save (data-l10n updated too) and a Cancel button appears; submit
  updates the entry in place, recomputing fid/parentFid and excluding
  the edited row from the duplicate-path check
- Delete removes without confirmation; deleting the row being edited
  cancels the edit and an earlier deletion shifts the edit index
- pysimCustomAdd renamed to pysimCustomSubmit; tests for the whole
  flow; SW cache v114 -> v115.

frontend/tests/html.test.js

@@ -54,3 +54,10 @@ test('file manager has FID / Name sort pills', () => {
     assert.match(html, /data-fs-sort="name" onclick="pysimFsSetSort\('name'\)"/);
     assert.ok(html.includes('pysim-fs-sort-pill'));
 });
+
+test('custom files form has add/save and cancel controls', () => {
+    assert.match(html, /id="pysim-cf-add-btn"[^>]*data-l10n="Add"/);
+    assert.match(html, /id="pysim-cf-cancel-btn"[^>]*class="hidden[^"]*"[^>]*data-l10n="Cancel"/);
+    assert.ok(html.includes("event.key==='Enter')pysimCustomSubmit()"));
+    assert.ok(!html.includes('pysimCustomAdd'));
+});