M4 — channel browse + context-menu drill-down

Sidecar ChannelVideos op via rustypipe channel_videos(). Returns the
channel metadata block (id, name, subscribers, banner) alongside the
items array — same VideoItem shape as search.

Addon refactor: _add_video_items is now the shared listing builder.
Both _search_directory and _channel_directory call it. Each video
result gets a 'Go to <channel>' context-menu entry that
Container.Update's to ?action=channel&id=<channel_id> — so from any
search result, the user can drill into that channel's recent uploads
without going back through search.

Smoke verified on the Pi via Files.GetDirectory: LTT channel
(UCXuqSBlHAE6Xw-yeJA0Tunw) returned 30 recent videos.

Addon version 0.0.7.

MILESTONES.md

@@ -43,9 +43,11 @@
       `IsPlayable=true`, thumbnails, video InfoLabels
 - [x] verified via JSON-RPC: `Files.GetDirectory` returns 19+ formatted
       results for "linus tech tips"
-- [ ] channel browse → `{"op":"channel_videos","id":"…"}`
+- [x] channel browse → `{"op":"channel_videos","id":"…"}` — verified 30
+      videos returned for LTT's UCXuqSBlHAE6Xw-yeJA0Tunw via JSON-RPC
+- [x] context-menu entry on every result: "Go to <channel>" → channel listing
 - [ ] playlist browse → `{"op":"playlist","id":"…"}`
-- [ ] paginated results (currently capped at limit=30)
+- [ ] paginated results (currently capped at limit=30/50)
 - [ ] search history
 
 ## M5 — SponsorBlock skipping [DONE]