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/scheduler.ts

@@ -3,6 +3,7 @@ import { childLogger } from "./util/logger.js";
 import { withTdlibMutex } from "./util/mutex.js";
 import { getActiveAccounts, getPendingAccounts } from "./db/queries.js";
 import { runWorkerForAccount, authenticateAccount } from "./worker.js";
+import { runIntegrityAudit } from "./audit.js";
 
 const log = childLogger("scheduler");
 
@@ -87,6 +88,16 @@ async function runCycle(): Promise<void> {
       { elapsed: Math.round((Date.now() - cycleStart) / 1000) },
       "Ingestion cycle complete"
     );
+
+    // Run integrity audit after all accounts are processed
+    try {
+      const auditResult = await runIntegrityAudit();
+      if (auditResult.issues > 0) {
+        log.info({ ...auditResult }, "Integrity audit found issues");
+      }
+    } catch (auditErr) {
+      log.warn({ err: auditErr }, "Integrity audit failed");
+    }
   } catch (err) {
     log.error({ err }, "Ingestion cycle failed");
   } finally {