chore(backlog): maintain task backlog and add changelog fragments

- Move completed tasks (85, 117, 118, 155) to backlog/completed/
- Delete superseded task files (166 verification, 172 drilldown)
- Add stats dashboard milestone m-1
- Add new tasks (190, 194)
- Update task metadata across remaining backlog items
- Add changelog fragments for stats, mpv args, and subtitle filtering

backlog/tasks/task-146 - Forward-overlay-Tab-to-mpv-for-AniSkip.md

@@ -5,14 +5,14 @@ status: Done
 assignee:
   - codex
 created_date: '2026-03-09 00:00'
-updated_date: '2026-03-16 05:13'
+updated_date: '2026-03-18 05:28'
 labels:
   - bug
   - overlay
   - aniskip
   - linux
 dependencies: []
-ordinal: 46500
+ordinal: 47500
 ---
 
 ## Description