feat(FN-2471): persist source issue provenance in task storage

- Add TaskSourceIssue contract and thread sourceIssue through Task, TaskCreateInput, archived task entries, and TaskStore serialization paths.
- Extend SQLite schema to v45 with sourceIssue* columns and add migration coverage for v44 upgrades plus legacy JSON migration import.
- Persist, update, clear, and archive/unarchive sourceIssue metadata in TaskStore with dedicated regression tests.
- Update core and dashboard tests to schema v45 expectations and stabilize flaky modal assertions with async waits.

packages/core/src/__tests__/task-documents.test.ts

@@ -51,7 +51,7 @@ describe("TaskStore task documents", () => {
 
     expect(tableNames.has("task_documents")).toBe(true);
     expect(tableNames.has("task_document_revisions")).toBe(true);
-    expect(db.getSchemaVersion()).toBe(44);
+    expect(db.getSchemaVersion()).toBe(45);
 
     const index = db
       .prepare(