fix(plugins): restore window.esc for out-of-tree plugins (#986)

app.js exported `esc` as an implicit global back when it was a classic
script. a9fce29 made it an ES module and 14b4058 carved `esc` into
js/dom.js; the window re-export list was rebuilt without it.

Out-of-tree plugins load screen.js as a classic script and call `esc()`
bare, so nothing in-tree catches the break: no-undef, a call-graph scan
and a grep all pass while the plugin throws in the field. The MIDI
plugin builds its device list with esc() inside the same try block that
catches requestMIDIAccess() failures, so the ReferenceError surfaced to
testers as "MIDI Access denied esc is not defined" — access had actually
been granted.

Pin the whole plugin-facing global surface by name, mirroring
tests/test_plugin_context_contract.py. Verified both ways against a
running app: without the fix the spec fails with "missing or not
functions: esc".

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

static/app.js

@@ -2319,11 +2319,14 @@ configureHost({
     currentFilename: () => currentFilename,
 });
 
+// `esc` is here for out-of-tree plugins only: their screen.js loads as a classic
+// script and called esc() back when app.js was one too and it was an implicit
+// global. Nothing in core reads window.esc — import it from ./js/dom.js instead.
 Object.assign(window, {
     _confirmDialog, _getArrangementNamingMode, _libraryLocalFilename, _librarySongArtUrl,
     _librarySongId, _onHeaderClick, _onNamingModeChange, _trapFocusInModal,
     changeArrangement, checkPluginUpdates, clearLibFilters, clearLoop,
-    deleteSelectedLoop, exportDiagnostics, exportSettings, filterFavorites,
+    deleteSelectedLoop, esc, exportDiagnostics, exportSettings, filterFavorites,
     filterLibrary, fullRescanLibrary, goFavPage, handleSliderInput,
     hideScanBanner, importSettings, loadPlugins, loadSavedLoop,
     loadSettings, onSectionPracticeModeChange, openEditModal, persistSetting,