Replaces the six noisy per-day stacked-area charts in the stats
Trends tab with a single "Library — Summary" section: a top-10
watch-time leaderboard plus a sortable per-title table. Scoped
to the existing date range selector; integrates with the shared
visibility filter.
Task-by-task TDD plan for the seven items in the matching design
spec, organized as eleven commits in a single PR (365d backend,
server allow-list, frontend selector, vocabulary column,
Anki-deleted card filter, library episode delete, collapsible
library groups, session grouping helper, sessions tab rollup,
chart clarity pass, changelog fragment).
Design for a single PR covering seven stats dashboard items:
collapsible library series groups, same-episode session rollups,
365d trend range, episode delete in library detail, tighter
vocabulary word/reading column, filtering Anki-deleted cards, and
a chart clarity pass with shared theming.
