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/tdlib/download.ts

@@ -51,6 +51,10 @@ interface TdMessage {
           path?: string;
           is_downloading_completed?: boolean;
         };
+        remote?: {
+          /** Stable identifier across reposts of the same file content. */
+          unique_id?: string;
+        };
       };
     };
     photo?: {
@@ -231,6 +235,7 @@ export async function getChannelMessages(
             mediaAlbumId: msg.media_album_id && msg.media_album_id !== "0" ? msg.media_album_id : undefined,
             replyToMessageId: msg.reply_to_message_id ? BigInt(msg.reply_to_message_id) : undefined,
             caption: msg.content?.caption?.text || undefined,
+            remoteUniqueId: doc.document.remote?.unique_id || undefined,
           });
           continue;
         }