S01 — Server-Side Pagination:
- Added getChannelContentPaginated() to content repository with search, filter, sort
- Channel content API now supports ?page, ?pageSize, ?search, ?status, ?contentType, ?sortBy, ?sortDirection
- Backwards-compatible: no params returns all items (legacy mode)
- Frontend useChannelContentPaginated hook with keepPreviousData
- ChannelDetail page: search bar, status/type filter dropdowns, pagination controls
- Sorting delegated to server (removed client-side sortedContent)
- Item count shown in Content header (e.g. '121 items')
S04 — Download Engine Hardening:
- yt-dlp auto-update on production startup (native -U with pip fallback)
- Error classification: rate_limit, format_unavailable, geo_blocked, age_restricted, private, network
- Format fallback chains: preferred res → best under res → single best → any
- Improved parseFinalPath: explicit non-path prefix detection, extension validation
- Error category included in download:failed events
- classifyYtDlpError() exported from yt-dlp module for downstream use
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