feat: group merge, ZIP/reply/caption grouping, integrity audit

Group merge UI:
- Add mergeGroups query and mergeGroupsAction server action
- Add "Start Merge" / "Merge Here" buttons to group row actions
- Two-step UX: click Start on source, click Merge Here on target

ZIP path prefix grouping (Signal 7):
- Compare PackageFile.path root folders across ungrouped packages
- Auto-group if 2+ packages share the same dominant root folder

Reply chain grouping (Signal 6):
- Capture reply_to_message_id during channel scanning
- Group archives that reply to the same root message
- Add replyToMessageId field to Package schema

Caption fuzzy match grouping (Signal 8):
- Capture source caption during channel scanning
- Normalize captions (strip extensions, extract significant words)
- Group packages with matching normalized caption keys
- Add sourceCaption field to Package schema

Periodic integrity audit:
- Check multipart packages for completeness (parts vs destMessageIds)
- Detect orphaned indexes (destChannelId set but no destMessageId)
- Runs after each ingestion cycle, deduplicates notifications

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

src/lib/telegram/queries.ts

@@ -736,3 +736,13 @@ export async function dissolveGroup(groupId: string) {
   });
   await prisma.packageGroup.delete({ where: { id: groupId } });
 }
+
+export async function mergeGroups(targetGroupId: string, sourceGroupId: string) {
+  // Move all packages from source group to target group
+  await prisma.package.updateMany({
+    where: { packageGroupId: sourceGroupId },
+    data: { packageGroupId: targetGroupId },
+  });
+  // Delete the now-empty source group
+  await prisma.packageGroup.delete({ where: { id: sourceGroupId } });
+}