fix: address post-audit regressions across queue, db, and ui

- Preserved extension-captured cookies through the Add modal, with a clean fallback when captured cookies break metadata fetching.
- Prevented batched extension captures from losing URLs or reusing stale cookie/header contexts.
- Fixed pause/resume and enqueue generation races, including cancellation during queue reservation and replay after task removal.
- Made startup database initialization safe under React StrictMode.
- Serialized keyring operations and corrected Linux legacy migration/deletion behavior.
- Restored `Downloading` state after yt-dlp retries.
- Replaced hardcoded media heights with dynamically detected formats, including nonstandard qualities such as 576p and 2880p.

src/utils/addDownloadMetadata.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from 'vitest';
 import {
+  appendRequestUrlsAfterVersion,
   canSubmitMetadataRows,
   mediaFormatSelectorForRow,
   mediaFileNameForSelectedFormat,
@@ -93,6 +94,7 @@ describe('add download metadata workflow', () => {
       status: 'ready',
       generation: 4,
       requestContextVersion: 1,
+      requestCookiesOmitted: true,
       formats: [{
         name: '1080p MP4',
         selector: '137+140',
@@ -119,11 +121,30 @@ describe('add download metadata workflow', () => {
       status: 'loading',
       generation: 5,
       requestContextVersion: 2,
+      requestCookiesOmitted: false,
       formats: undefined,
       selectedFormat: undefined
     });
   });
 
+  it('appends every unseen handoff after the observed version', () => {
+    const merged = appendRequestUrlsAfterVersion(
+      'https://existing.example/file.zip',
+      {
+        'https://first.example/file.zip': { version: 2 },
+        'https://second.example/file.zip': { version: 3 },
+        'https://existing.example/file.zip': { version: 4 }
+      },
+      1
+    );
+
+    expect(merged).toBe(
+      'https://existing.example/file.zip\n' +
+      'https://first.example/file.zip\n' +
+      'https://second.example/file.zip'
+    );
+  });
+
   it('upgrades an existing normal row when the user explicitly fetches it as media', () => {
     const existing = row({
       sourceUrl: 'https://adult.example/watch/123',