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>

worker/src/db/queries.ts

@@ -119,6 +119,8 @@ export interface CreatePackageInput {
   tags?: string[];
   previewData?: Buffer | null;
   previewMsgId?: bigint | null;
+  sourceCaption?: string | null;
+  replyToMessageId?: bigint | null;
   files: {
     path: string;
     fileName: string;
@@ -150,6 +152,8 @@ export async function createPackageWithFiles(input: CreatePackageInput) {
       tags: input.tags && input.tags.length > 0 ? input.tags : undefined,
       previewData: input.previewData ? new Uint8Array(input.previewData) : undefined,
       previewMsgId: input.previewMsgId ?? undefined,
+      sourceCaption: input.sourceCaption ?? undefined,
+      replyToMessageId: input.replyToMessageId ?? undefined,
       files: {
         create: input.files,
       },
@@ -613,7 +617,7 @@ export async function createAutoGroup(input: {
   sourceChannelId: string;
   name: string;
   packageIds: string[];
-  groupingSource: "AUTO_TIME" | "AUTO_PATTERN" | "AUTO_ZIP" | "AUTO_CAPTION";
+  groupingSource: "AUTO_TIME" | "AUTO_PATTERN" | "AUTO_ZIP" | "AUTO_CAPTION" | "AUTO_REPLY";
 }): Promise<string> {
   const group = await db.packageGroup.create({
     data: {