Implement fit-mode rendering contract with container sizing and pane re-fit

src/app/orchestration/preferences.ts

@@ -0,0 +1,26 @@
+/**
+ * Preference orchestration — bridges the (browser-free) AppStore to the settings
+ * adapter for the small UI preferences pulled forward ahead of the M5 Settings
+ * modal. Same store↔adapter pattern as theme orchestration; currently the only
+ * such preference is the Live Preview fit mode (spec §04, `previewFitMode`).
+ *
+ * Unlike theme there is no FOUC concern (the preview renders after hydration
+ * anyway), but hydrating early keeps the store the single source of truth from
+ * the first render.
+ */
+
+import { loadPreviewFitMode, savePreviewFitMode } from '../infrastructure/settings-store';
+import { useAppStore } from '../stores/AppStore';
+
+/** Hydrate the persisted fit mode into the store. Call before render. */
+export function initPreviewFitMode(): void {
+  useAppStore.getState().setPreviewFitMode(loadPreviewFitMode());
+}
+
+/** Persist the fit mode on change. Returns a teardown that detaches the subscriber. */
+export function wirePreviewFitMode(): () => void {
+  return useAppStore.subscribe((state, prev) => {
+    if (state.previewFitMode === prev.previewFitMode) return;
+    savePreviewFitMode(state.previewFitMode);
+  });
+}