Fix nested comments not displaying on comment view page

When opening a comment directly via URL, nested replies were not shown.
The pagination logic hardcoded depth === 1, assuming we're always viewing
the main post. Changed to use postData.depth + 1 to correctly find direct
replies regardless of the current post/comment depth.

Fixes #769

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>