Fix crxjs dev service worker crashes after Vite upgrade.

Downgrade to Vite 6 with crxjs 2.6, add dev-only CSP for HMR, and stop the background script from importing Svelte plugin UI into the service worker.

src/plugins/syncablePluginDefaults.ts

@@ -0,0 +1,41 @@
+/**
+ * Serializable plugin setting defaults for cloud sync backfill.
+ *
+ * Kept separate from `@/plugins` so the service worker never imports Svelte UI or
+ * Vite HMR clients. Values must match each plugin's non-component settings.
+ */
+function defaultSearchHotkey(): string {
+  if (typeof navigator !== "undefined") {
+    return navigator.platform.toUpperCase().includes("MAC") ? "cmd+k" : "ctrl+k";
+  }
+  return "ctrl+k";
+}
+
+/** `plugin.<id>.settings` defaults (component/button keys omitted). */
+export const SYNCABLE_PLUGIN_SETTING_DEFAULTS: Record<
+  string,
+  Record<string, unknown>
+> = {
+  themes: {},
+  "animated-background": { speed: 1 },
+  "assessments-average": { lettergrade: false },
+  notificationCollector: {},
+  timetable: {},
+  timetableEdit: {},
+  "profile-picture": { useCloudPfp: false },
+  "assessments-overview": {},
+  "background-music": { volume: 0.5, pauseOnHidden: true },
+  messageFolders: {
+    showTagsInAllMessages: true,
+    hideFolderedMessagesInAll: true,
+  },
+  "enhanced-navigation": { autoScrollOnClick: false },
+  "global-search": {
+    searchHotkey: defaultSearchHotkey(),
+    showRecentFirst: true,
+    transparencyEffects: true,
+    runIndexingOnLoad: true,
+    passiveIndexing: true,
+  },
+  "grade-analytics": { cacheTtlHours: 24 },
+};