fix(core): sync review round 1: lists, supersede, dedupe conflicts, retries

- dedupe files conflicts for disagreeing fields instead of dropping them
- merged-away records never file removals
- matched work committed before apply so retries reuse it (no draft leaks)
- stale pending events superseded by newer values
- multi-source engagement removal only detaches the source
- list records applied with history-derived ownership
- gone targets resolve as ignored; counts only for committed records

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/test/sync/helpers.ts

@@ -108,3 +108,7 @@ export async function entryFor(db: Db, userId: string, isbn: string) {
     .executeTakeFirst();
   return row ? { ...row, fieldSources: JSON.parse(row.field_sources) as Record<string, string> } : undefined;
 }
+
+export function listRec(key: string, name: string, items: { work: WorkHint; note?: string }[], description?: string): SourceRecord {
+  return { key, kind: "list", list: { name, items, ...(description !== undefined ? { description } : {}) }, raw: { key } };
+}