feat(web): honest sparse-state and queue copy

Make the sparse reality legible instead of implying abundance or imminence
(UX review A1-A4, A6):

- Empty-connected state drops the impossible "Run `tapir run`" instruction
  (no shell for web users; discovery is in-process since ADR-018) for a
  passive "summaries appear gradually, check back later".
- Pipeline bar reframes counts by what the user can do: "N ready · M in queue
  · K no captions" (was "summarized / fetching soon / pending").
- A one-line note explains captions are fetched slowly on purpose to respect
  YouTube's limits — turning confusing emptiness into intentional design.
- Card state for throttled videos reads "In queue", not "Fetching soon…"
  (256 items behind a per-IP gate are not all imminent — ADR-014).
- Quiet nudge button drops the over-promising "now": "Summarize", not
  "Summarize now". On click the card still honestly becomes "Queued".
- Queued card says "summarizing shortly", not "waiting for the next run"
  (no scheduler jargon).

Pure copy/label — no logic, DB, or fetch-rate change. The rate gate is
untouched; scarcity is surfaced, never engineered around.

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

internal/web/view.go

@@ -538,6 +538,7 @@ a.btn, a.btn:visited { color: var(--accent-fg); }
 .pipeline-bar { display: flex; gap: var(--s3); align-items: center; flex-wrap: wrap; margin-bottom: var(--s3); font-size: .8rem; color: var(--muted); }
 .pipeline-bar span { display: flex; align-items: center; gap: var(--s1); }
 .pipeline-bar span + span::before { content: "·"; margin-right: var(--s1); }
+.pipeline-note { margin: calc(-1 * var(--s2)) 0 var(--s3); font-size: .8rem; line-height: 1.5; max-width: 40rem; }
 .card-nudge-form { display: inline; }
 .btn-quiet { font: inherit; font-size: .72rem; font-weight: 600; padding: .15rem .55rem; border-radius: 999px; border: 1px solid var(--accent); background: transparent; color: var(--accent); cursor: pointer; }
 .btn-quiet:hover { background: var(--accent-weak); }