perf: move PouchDB/IndexedDB operations to a Web Worker

All database reads and writes now run off the main thread via a
dedicated worker, eliminating IndexedDB overhead from the frame budget.

- Create data.worker.ts exposing the Data class via Comlink
- Refactor data.ts to export a Comlink-wrapped proxy and a standalone
  generateId() pure function (workers can't expose sync methods cleanly)
- Update all 10 call sites to import generateId directly instead of
  calling data.generateId()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/modules/card/hooks/useSpacedRepetitionCards.ts

@@ -4,7 +4,7 @@ import { useAsyncState } from "@vueuse/core"
 import { addDays, isAfter } from "date-fns"
 import { computed, nextTick, watch } from "vue"
 
-import { data } from "@/data/data"
+import { data, generateId } from "@/data/data"
 import { DataType } from "@/data/DataType.enum"
 import { useFile } from "@/hooks/useFile.hook"
 import { useLinks } from "@/hooks/useLinks.hook"
@@ -51,7 +51,7 @@ export const useSpacedRepetitionCards = () => {
         const repetition = await data.getOrCreate<
           DataType.RepetitionCard,
           RepetitionCard
-        >(data.generateId(DataType.RepetitionCard, cardFile.path), {
+        >(generateId(DataType.RepetitionCard, cardFile.path), {
           $type: DataType.RepetitionCard,
           level: 1,
           repeatDate: new Date(),