feat(db): add attemptCount on SkippedPackage + CHANNEL_ACCESS_LOST enum

attemptCount tracks how many times the worker has tried each failed
source message. Combined with WORKER_MAX_SKIP_ATTEMPTS (default 5), the
worker will auto-retry across cycles but eventually let the watermark
advance past a chronically failing file so cycles aren't pinned forever.
The SkippedPackage row stays so the user can manually retry via the UI.

CHANNEL_ACCESS_LOST is a new notification type the worker emits when a
source channel becomes inaccessible (account got removed, channel
deleted, etc.) — surfaces the issue instead of silently failing every
cycle as we've been doing with "Iridium 2 w/ Add-ons [Completed]".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

prisma/migrations/20260522000000_skip_attempt_count_and_channel_access/migration.sql

@@ -0,0 +1,8 @@
+-- AlterTable: track how many times the worker has tried each skipped source message.
+-- Existing rows default to 1 (they represent a single past attempt that the worker
+-- chose to record). Future failures increment via upsertSkippedPackage.
+ALTER TABLE "skipped_packages" ADD COLUMN "attemptCount" INTEGER NOT NULL DEFAULT 1;
+
+-- AlterEnum: add CHANNEL_ACCESS_LOST so the worker can surface a notification
+-- when a source channel becomes inaccessible (account removed, channel deleted, etc.)
+ALTER TYPE "NotificationType" ADD VALUE 'CHANNEL_ACCESS_LOST';

prisma/schema.prisma

@@ -741,6 +741,12 @@ model SkippedPackage {
   sourceTopicId   BigInt?
   isMultipart     Boolean          @default(false)
   partCount       Int              @default(1)
+  /// How many times the worker has tried to process this source message.
+  /// The worker auto-retries failures across cycles up to a configurable cap
+  /// (WORKER_MAX_SKIP_ATTEMPTS, default 5). After the cap, the watermark is
+  /// allowed to advance past the failure so cycles aren't pinned forever;
+  /// the user can manually retry via the UI to reset and try again.
+  attemptCount    Int              @default(1)
   accountId       String
   account         TelegramAccount  @relation(fields: [accountId], references: [id], onDelete: Cascade)
   createdAt       DateTime         @default(now())
@@ -830,6 +836,7 @@ enum NotificationType {
   DOWNLOAD_FAILED
   GROUPING_CONFLICT
   INTEGRITY_AUDIT
+  CHANNEL_ACCESS_LOST
 }
 
 enum NotificationSeverity {