fix(youtube): Videos tab fallback misses lockupViewModel format

[FSpark]

Problem

After #1164 landed, opencli youtube channel <id> still returns empty recent_videos for channels whose Home tab is empty AND whose Videos tab uses the newer lockupViewModel InnerTube format.

Reproducer: opencli youtube channel @Jett.franzen (~207K subs, 216 videos). Returns 0 videos despite the Videos tab being fully populated.

Root cause

The Videos-tab fallback added in #1109 only parses item.richItemRenderer?.content?.videoRenderer (the legacy format). Many channels now return the newer lockupViewModel format from the Videos tab browse endpoint, which the fallback silently skips.

Meanwhile, the Home tab extraction (lines 101-118) already handles lockupViewModel, creating an inconsistency between the two code paths.

Concrete shape on the reproducer channel:

// Videos tab richGrid item — lockupViewModel (skipped)
{
  richItemRenderer: {
    content: {
      lockupViewModel: {
        contentType: 'LOCKUP_CONTENT_TYPE_VIDEO',
        contentId: 'G4ngHcS4aJs',
        metadata: { lockupMetadataViewModel: { title: { content: '...' }, ... } },
        contentImage: { thumbnailViewModel: { overlays: [/* duration badge */] } },
        ...
      }
    }
  }
}

Fix

Extract a shared parseVideoItem() helper that handles both lockupViewModel and videoRenderer formats, and use it in the Videos-tab fallback loop. This reuses the same parsing logic already proven in the Home tab path.

Changes:

• clis/youtube/channel.js: +32 lines (new parseVideoItem helper, updated fallback)
• clis/youtube/channel.test.js: +6 test cases for the new helper

Verification

$ opencli youtube channel @Jett.franzen --limit 10 -f json
# Before: returns metadata only, 0 videos
# After:  returns 10 videos with title, duration, views, url

npm test --project adapter passes (3418 / 3418).

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