feat: fix multi-part archive forwarding and add kickstarter package linking

Multi-part send fix:
- Add destMessageIds BigInt[] to Package schema with backfill migration
- Worker uploadToChannel now returns all message IDs, stored in DB
- Bot forwards all parts of multi-part archives (not just the first)
- Add retry logic for upload rate limits (429) and download stalls

Kickstarter package linking:
- Add package search/linking queries and API routes
- Add PackageLinkerDialog with search + checkbox selection
- Add "Link Packages" and "Send All" actions to kickstarter table
- Add sendAllKickstarterPackages server action

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/app/api/packages/linked/route.ts

@@ -0,0 +1,21 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/lib/auth";
+import { getLinkedPackageIds } from "@/data/kickstarter.queries";
+
+export const dynamic = "force-dynamic";
+
+export async function GET(request: Request) {
+  const session = await auth();
+  if (!session?.user?.id) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const { searchParams } = new URL(request.url);
+  const kickstarterId = searchParams.get("kickstarterId");
+  if (!kickstarterId) {
+    return NextResponse.json({ error: "kickstarterId required" }, { status: 400 });
+  }
+
+  const packageIds = await getLinkedPackageIds(kickstarterId);
+  return NextResponse.json({ packageIds });
+}