feat(persistence): bidirectional local/cloud story sync (Supabase)

Connect the previously-skeleton cloudStore to the client with a full
bidirectional reconcile engine. Commercial build (AUTH_ENABLED) only; the
open-source build is byte-for-byte unchanged — all cloud paths short-circuit
when AUTH_ENABLED is false.

- cloudSync.ts: reconcile engine — decideAction (pure, LWW rev->updatedAt with
  tombstone priority) + syncOnLogin/pushOnSave/pushDeletion (best-effort,
  serialized, isAuthed-gated)
- cloudSyncClient.ts: browser fetch bridge (short-circuit + fault-tolerant)
- /api/stories/{manifest,pull,push,delete}: RLS-guarded sync endpoints
- upsert_story_if_newer RPC: optimistic concurrency (SECURITY INVOKER,
  auth.uid() injection, rev->updated_at guard, revoked from public)
- cloudStore: +manifest/pullBlobs, save->RPC {stored,won}, softDelete w/ rev
- localStore: +listAllRecordsForSync/putSyncedRecord/markRecordSynced
  (concurrency-guarded sync writes); types: +StorySyncMeta/StorySyncEnvelope
- facade + UserChip: inject pushOnSave/pushDeletion + login-triggered reconcile

Sync model: full reconcile on login + background push on save (no Realtime;
eventual consistency). Conflict resolution: last-write-wins.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/api/stories/pull/route.ts

@@ -0,0 +1,33 @@
+import { NextResponse } from "next/server";
+import { requireUser } from "@/lib/supabase/guard";
+import { cloudPullBlobs } from "@/lib/persistence/cloudStore";
+
+export const runtime = "nodejs";
+
+// Cap per request — reconcile chunks its pull set, so one call never asks for an
+// unbounded id list (a denial-of-wallet / oversized-response guard).
+const MAX_PULL_IDS = 200;
+
+// POST /api/stories/pull — body { ids: string[] } → { blobs: StorySyncEnvelope[] }
+// (full payloads, INCLUDING tombstones, for write-back into the local store).
+// Pure passthrough to cloudStore; same auth/short-circuit story as manifest.
+export async function POST(req: Request) {
+  const auth = await requireUser();
+  if (auth instanceof NextResponse) return auth;
+
+  let body: { ids?: unknown };
+  try {
+    body = await req.json();
+  } catch {
+    return NextResponse.json({ error: "invalid json" }, { status: 400 });
+  }
+
+  const ids = Array.isArray(body.ids)
+    ? body.ids
+        .filter((x): x is string => typeof x === "string" && x.length > 0)
+        .slice(0, MAX_PULL_IDS)
+    : [];
+
+  const blobs = await cloudPullBlobs(ids);
+  return NextResponse.json({ blobs });
+}