feat(worker): use TDLib remote.unique_id as zero-false-positive dedup signal

The fileName + size repost detection from ff4e150 works but has a
theoretical false-positive: two unrelated files in the same channel
with identical names and identical total sizes get treated as duplicates.

TDLib's document.remote.unique_id is a stable identifier per file
content — every repost of the exact same file across messages keeps
the same unique_id. Using it as the first dedup check eliminates the
false-positive risk entirely.

Schema:
  - Package.remoteUniqueId (nullable, since existing rows lack it)
  - Index on (sourceChannelId, remoteUniqueId)

Pipeline:
  1. Capture remoteUniqueId in getChannelMessages + getTopicMessages
  2. Pass through TelegramMessage type
  3. processOneArchiveSet checks findPackageByRemoteUniqueId FIRST
     (before packageExistsBySourceMessage / findRepostedPackage)
  4. createPackageStub stores it on the new Package row

Existing 19,952 Packages have remoteUniqueId = NULL — they fall through
to the existing checks (source-msg-id, name+size, content-hash). New
ingestions populate it and benefit from the strong signal immediately.
Old Packages get backfilled organically when their content is
re-encountered and a new Package would otherwise be created.

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

worker/src/archive/multipart.ts

@@ -11,8 +11,11 @@ export interface TelegramMessage {
   fileSize: bigint;
   date: Date;
   mediaAlbumId?: string;
-  replyToMessageId?: bigint;  // NEW
-  caption?: string;            // NEW
+  replyToMessageId?: bigint;
+  caption?: string;
+  /** TDLib's `remote.unique_id` for the file — stable across reposts of
+   *  the exact same content. Empty string if the message didn't expose it. */
+  remoteUniqueId?: string;
 }
 
 export interface ArchiveSet {