docs: reconcile requirements + architecture with ADR-020

Bring the living docs current with the recency-bounded auto-summarize + sparse
honesty + feed IA bundle (ADR-020):

- requirements (BDD): summarize_mode.feature — auto now summarizes RECENT new
  videos; added a scenario for older videos (listed, on-demand), recency note.
- architecture.md: summarization-mode + new list-surface paragraph; scheduler
  diagram + two-path table + three-phase pass now show the recency pre-filter;
  dropped stale "Summarize now".
- data-model.md: auto_summarize is recent-only, older on-demand.
- README.md: one-line recency note on the serve scheduler.
- ui-spec.md: appended the as-built ADR-020 row (supersedes earlier copy/sort).
- specs/{video-card-states,newest-first-ordering,scheduled-discovery}.md:
  superseded/extended banners pointing at ADR-020 (kept as design records).

Docs-only; task check green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/specs/video-card-states.md

@@ -1,5 +1,12 @@
 # Spec — Unify video-card states: one "Summarize now" verb, honest no-captions state
 
+> **Superseded in part by ADR-020 (2026-06-08).** The five card states still hold, but the copy
+> changed: the nudge verb is now **"Summarize"** (not "Summarize now"), the rate-limited state
+> reads **"In queue"** (not "Fetching soon…"), and the queued state reads **"summarizing
+> shortly"** (not "waiting for the next run"). The list also now collapses older un-summarized
+> and caption-less videos. See `DECISIONS.md` ADR-020 and `views.templ` (`VideoCard`) for the
+> current copy; this doc is kept as the original design record.
+
 **Repo:** tapir · **Size:** small, **view-layer only** (`views.templ` + a little CSS in
 `view.go`; regenerate `views_templ.go`). No handler, store, or DB change. The two existing
 handlers (`/summarize`, `/retry-now`) stay exactly as they are — only what the card *shows*