feat: file upload from UI, notification dismiss, audit false positive fix

Manual file upload:
- Upload dialog in STL page with drag-and-drop file picker
- Files saved to shared Docker volume (/data/uploads)
- Worker processes via pg_notify('manual_upload') channel
- Hashes, reads metadata, splits >2GB, uploads to Telegram
- Multiple files automatically grouped
- Status polling shows upload/processing/complete states

Notification fixes:
- Add dismiss (X) button on each notification
- Add "Clear" button to remove all notifications
- Fix false positive MISSING_PART alerts from legacy packages
  (only flag when >1 destMessageIds stored but count wrong,
  not when only 1 ID from backfill)

Infrastructure:
- ManualUpload + ManualUploadFile schema + migration
- Shared manual_uploads Docker volume between app and worker
- Upload API routes (POST /api/uploads, GET /api/uploads/[id])
- Worker manual-upload processor with full pipeline

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

worker/src/audit.ts

@@ -38,7 +38,9 @@ export async function runIntegrityAudit(): Promise<{ checked: number; issues: nu
 
   for (const pkg of multipartPackages) {
     const actualParts = pkg.destMessageIds.length;
-    if (actualParts > 0 && actualParts !== pkg.partCount) {
+    // Only flag when we have >1 stored IDs but count doesn't match.
+    // Packages with exactly 1 ID are legacy (backfilled from single destMessageId) — not actionable.
+    if (actualParts > 1 && actualParts !== pkg.partCount) {
       issues++;
 
       // Check if we already have a notification for this