Introduce gated logo loading system that ensures logos render after both
ChannelsTable and StreamsTable have completed their initial data fetch,
preventing visual race conditions and ensuring proper paint order.
Changes:
- Add `allowLogoRendering` flag to logos store to gate logo fetching
- Implement `onReady` callbacks in ChannelsTable and StreamsTable
- Add orchestration logic in Channels.jsx to coordinate table readiness
- Use double requestAnimationFrame to defer logo loading until after browser paint
- Remove background logo loading from App.jsx (now page-specific)
- Simplify fetchChannelAssignableLogos to reuse fetchAllLogos
- Remove logos dependency from ChannelsTable columns to prevent re-renders
This ensures visual loading order: Channels → EPG → Streams → Logos,
regardless of network speed or data size, without timer-based hacks.
