feat: Dayparting PR 1/5 — foundation (db/35, Show entity + /api/shows, resolver chokepoint, air-time stamp)

[genwave-radio]

📛 Dayparting epic — PR 1 of 5 (SPEC F115–F121 · PLAN T238–T242)

Zero audible change — the foundation every later PR stands on:

• 🗄️ db/35 (35-show-identity-migration.sh + db/06 + 01-library fresh-init mirrors): station.show widens — slug (unique show_slug_key), tagline, flavor (prompt-only, never public), provenance, and the dormant persona_id/envelope bundle columns (ruled 2026-08-10 — unread until the schedulable-bundle slice; layering rule recorded: block ?? show ?? none, block wins). Plus booth_log.show_id + library.media.show_id (both deliberately no-FK — F121.1 history / db/22 grant boundary).
• 🎛️ Show domain + /api/shows (T239/T240): budgets 60/120/400 at the seam, house Slugify (FallbackSlug promoted), 23503→Referenced mapped store-side (T120 ruling), delete guard 409 naming referencing blocks, best-effort imaging unscope (post-commit, CancellationToken.None, logged), F115.5 write gate (authored save never erases imported provenance) + gh-save-as-own provenance guard is read-then-write (TOCTOU) — make it a conditional upsert #394 note. New IShowImagingScope seam — SEAMS.md 77→79 (generated).
• 🎯 EffectiveAssignment chokepoint (T241): ONE identity function in ScheduleResolver; OnAirSnapshot/ScheduleSegment gain ShowSummary (Abstractions — source-compatible trailing defaults per the MediaItem/SegmentRequest precedent); schedule load LEFT JOINs exactly 4 show columns (the dormant pin is structural — ShowSummary has no member to receive them).
• 🧾 Air-time show_id stamp (T242): publish-time capture (the T60 discipline, backlog-proven) via an ActiveShowId DIM on IActivePersonaAccessor; one chokepoint stamps music + kinded alike; tools/demo_hour_gate.sql gains the F121.2 halves (recurring-show false-pass closed via lag() bounding; coalesce false — both probe-proven red/green). Rider: IBoothLogAppender 8-positional-param → BoothLogAppendRequest (the recorded T220 carry-forward).

✅ Gates

Every task opus-review-gated (T238 ×4 rounds, T239 ×2, T240 ×2, T241 ×2, T242 ×2 — every catch mutation- or probe-proven). Suites: solution non-Integration green 0 failed, MediaLibrary Integration 647/0, Architecture laws 95/95, check-seam-index.sh green, -warnaserror 0/0. Kestrel-smoked: login → create → 409-naming-blocks (real FK) → delete, plus the JOIN'd schedule load, all through the production binary against live Postgres.

⚠️ Noted for the tracker (pre-existing, surfaced during review): Story012's 3s feeder-tick wall-clock budget flakes under parallel-suite load (~1 in 5 on a loaded box).

Stack: PR 2 (authoring surfaces) → PR 3 (on-air + spectator) → PR 4 (catalog) → PR 5 (specials, droppable) follow on this base.