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/audit.ts

@@ -0,0 +1,117 @@
+import { db } from "./db/client.js";
+import { childLogger } from "./util/logger.js";
+
+const log = childLogger("audit");
+
+/**
+ * Periodic integrity audit: checks all packages for consistency.
+ * Creates SystemNotification records for any issues found.
+ *
+ * Checks performed:
+ * 1. Multipart completeness: destMessageIds.length should match partCount
+ * 2. Missing destination: packages with destChannelId but no destMessageId
+ */
+export async function runIntegrityAudit(): Promise<{ checked: number; issues: number }> {
+  log.info("Starting integrity audit");
+
+  let checked = 0;
+  let issues = 0;
+
+  // Check 1: Multipart packages with wrong number of destination message IDs
+  const multipartPackages = await db.package.findMany({
+    where: {
+      isMultipart: true,
+      partCount: { gt: 1 },
+      destMessageId: { not: null },
+    },
+    select: {
+      id: true,
+      fileName: true,
+      partCount: true,
+      destMessageIds: true,
+      sourceChannelId: true,
+      sourceChannel: { select: { title: true } },
+    },
+  });
+
+  checked += multipartPackages.length;
+
+  for (const pkg of multipartPackages) {
+    const actualParts = pkg.destMessageIds.length;
+    if (actualParts > 0 && actualParts !== pkg.partCount) {
+      issues++;
+
+      // Check if we already have a notification for this
+      const existing = await db.systemNotification.findFirst({
+        where: {
+          type: "MISSING_PART",
+          context: { path: ["packageId"], equals: pkg.id },
+        },
+        select: { id: true },
+      });
+
+      if (!existing) {
+        await db.systemNotification.create({
+          data: {
+            type: "MISSING_PART",
+            severity: "WARNING",
+            title: `Incomplete multipart: ${pkg.fileName}`,
+            message: `Expected ${pkg.partCount} parts but only ${actualParts} destination message IDs stored`,
+            context: {
+              packageId: pkg.id,
+              fileName: pkg.fileName,
+              expectedParts: pkg.partCount,
+              actualParts,
+              sourceChannelId: pkg.sourceChannelId,
+              channelTitle: pkg.sourceChannel.title,
+            },
+          },
+        });
+
+        log.warn(
+          { packageId: pkg.id, fileName: pkg.fileName, expected: pkg.partCount, actual: actualParts },
+          "Multipart package has mismatched part count"
+        );
+      }
+    }
+  }
+
+  // Check 2: Packages with dest channel but no dest message (orphaned index)
+  const orphanedCount = await db.package.count({
+    where: {
+      destChannelId: { not: null },
+      destMessageId: null,
+    },
+  });
+
+  if (orphanedCount > 0) {
+    issues++;
+
+    const existing = await db.systemNotification.findFirst({
+      where: {
+        type: "INTEGRITY_AUDIT",
+        context: { path: ["check"], equals: "orphaned_index" },
+        createdAt: { gte: new Date(Date.now() - 24 * 60 * 60 * 1000) },
+      },
+      select: { id: true },
+    });
+
+    if (!existing) {
+      await db.systemNotification.create({
+        data: {
+          type: "INTEGRITY_AUDIT",
+          severity: "INFO",
+          title: `${orphanedCount} packages with missing destination message`,
+          message: `Found ${orphanedCount} packages that have a destination channel set but no destination message ID. These may be from interrupted uploads.`,
+          context: {
+            check: "orphaned_index",
+            count: orphanedCount,
+          },
+        },
+      });
+    }
+  }
+
+  log.info({ checked, issues }, "Integrity audit complete");
+  return { checked, issues };
+}