refactor(static): load the image editor on first use (#6074)

galleryEditor.js and its js/editor/ graph are 54 modules / 576 KB, and
gallery.js imported them statically. Every page load paid for the whole
image editor even though most sessions never open the Edit tab: 54 of the
173 JS files on a cold load, and 576 KB of the decoded JS, were for a
panel that was never displayed.

Add a small panel-loader registry (static/js/panels.js) that imports a
panel's module on first use and memoises the promise, so a double-click
cannot start two loads and a failed load can still be retried. Convert
the image editor to it, and route the two existing dynamic imports in
chat.js and chatRenderer.js through the same entry so all three call
sites share one module instance instead of two.

closeEditor() and isEditorOpen() stay synchronous: if the module was
never loaded there is no edit session to close and none can be open.

The service worker keeps precaching the editor, in a separate
PANEL_PRECACHE list, so the panel stays available offline even though
index.html no longer loads it. The two lists now serve different
purposes and the header comment says so.

static/sw.js

@@ -7,11 +7,22 @@
 //   - Other static assets (images/fonts/libs): cache-first with bg refresh.
 //   - API / non-GET: never cached.
 // Bump CACHE_NAME whenever the precache list or SW logic changes.
-const CACHE_NAME = 'odysseus-v376-settings-title-icons';
+const CACHE_NAME = 'odysseus-v377-lazy-image-editor';
 
-// Core shell precached on install so repeat opens are instant without any
-// network wait. Keep this list in sync with the <script type="module"> tags
-// and <link rel="stylesheet"> in index.html.
+// Two lists, two jobs — they are no longer the same set and must not be
+// "resynced" back into one:
+//
+//   PRECACHE       = the app shell. Mirrors the <script type="module"> tags
+//                    and <link rel="stylesheet"> in index.html — i.e. what
+//                    loads before first paint.
+//   PANEL_PRECACHE = modules that index.html deliberately does NOT load,
+//                    because js/panels.js imports them on first use. They are
+//                    off the critical path, not out of the offline manifest:
+//                    without them here, a panel the user never opened while
+//                    online could not open offline at all.
+//
+// Both are fetched at install time, in the background. Entries must match the
+// exact URL the browser requests, query string included.
 const PRECACHE = [
   '/',
   '/static/style.css',
@@ -63,13 +74,73 @@ const PRECACHE = [
   '/static/lib/highlight.min.js',
 ];
 
+// Lazily-imported panel modules (js/panels.js). Not in index.html by design;
+// precached so the panel still opens with no network.
+const PANEL_PRECACHE = [
+  // Image editor — galleryEditor.js and its js/editor/ graph.
+  '/static/js/galleryEditor.js',
+  '/static/js/editor/ai-inpaint.js?v=20260708match1',
+  '/static/js/editor/ai-models.js',
+  '/static/js/editor/ai-rembg.js',
+  '/static/js/editor/ai-tool-runner.js',
+  '/static/js/editor/ai-tools-misc.js',
+  '/static/js/editor/build/controls.js?v=20260708match1',
+  '/static/js/editor/build/popups.js',
+  '/static/js/editor/build/right-panel.js',
+  '/static/js/editor/build/toolbar.js?v=20260708sam3',
+  '/static/js/editor/build/topbar.js',
+  '/static/js/editor/build/transform-popup.js',
+  '/static/js/editor/canvas-coords.js',
+  '/static/js/editor/canvas-events.js',
+  '/static/js/editor/canvas-transforms.js',
+  '/static/js/editor/checkerboard.js',
+  '/static/js/editor/clipboard-and-drop.js',
+  '/static/js/editor/composite-helpers.js',
+  '/static/js/editor/filters/blur.js',
+  '/static/js/editor/filters/edge-feather.js',
+  '/static/js/editor/fx/adj-popup.js',
+  '/static/js/editor/fx/filter-string.js',
+  '/static/js/editor/fx/histogram.js',
+  '/static/js/editor/fx/pixel-pass.js',
+  '/static/js/editor/harmonize-masks.js',
+  '/static/js/editor/history-panel.js',
+  '/static/js/editor/keyboard-shortcuts.js',
+  '/static/js/editor/layer-helpers.js',
+  '/static/js/editor/layer-panel.js',
+  '/static/js/editor/mask-utils.js',
+  '/static/js/editor/shortcuts-popover.js',
+  '/static/js/editor/slider-ux.js',
+  '/static/js/editor/snap.js',
+  '/static/js/editor/state.js',
+  '/static/js/editor/stroke-pipeline.js',
+  '/static/js/editor/stroke-tool-sliders.js',
+  '/static/js/editor/tools/clone.js',
+  '/static/js/editor/tools/crop.js',
+  '/static/js/editor/tools/flood-fill.js',
+  '/static/js/editor/tools/lasso-mask.js',
+  '/static/js/editor/tools/lasso.js',
+  '/static/js/editor/tools/move.js',
+  '/static/js/editor/tools/stroke.js',
+  '/static/js/editor/tools/transform-drag.js',
+  '/static/js/editor/tools/transform-handles.js',
+  '/static/js/editor/tools/transform-session.js',
+  '/static/js/editor/tools/wand.js',
+  '/static/js/editor/wire-import.js',
+  '/static/js/editor/wire-inpaint-controls.js?v=20260708match1',
+  '/static/js/editor/wire-merge-buttons.js',
+  '/static/js/editor/wire-selection-controls.js',
+  '/static/js/editor/wire-topbar-menus.js',
+  '/static/js/editor/wire-topbar-overflow.js',
+  '/static/js/editor/wire-topbar.js',
+];
+
 self.addEventListener('install', (e) => {
   e.waitUntil(
     caches.open(CACHE_NAME).then(cache =>
       // addAll is atomic — if any item fails, none are cached. Use individual
       // puts so a single 404 can't block the whole install.
       Promise.all(
-        PRECACHE.map(url =>
+        [...PRECACHE, ...PANEL_PRECACHE].map(url =>
           fetch(url, { cache: 'reload' })
             .then(res => res.ok ? cache.put(url, res) : null)
             .catch(() => null)