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>

prisma/migrations/20260326120000_add_dest_message_ids/migration.sql

@@ -0,0 +1,7 @@
+-- AlterTable
+ALTER TABLE "packages" ADD COLUMN "destMessageIds" BIGINT[] DEFAULT ARRAY[]::BIGINT[];
+
+-- Backfill: copy existing destMessageId into the array
+UPDATE "packages"
+SET "destMessageIds" = ARRAY["destMessageId"]
+WHERE "destMessageId" IS NOT NULL;