feat: Dayparting PR 2/5 — authoring surfaces (Shows page, span-assign picker, imaging scope)

[genwave-radio]

📛 Dayparting epic — PR 2 of 5 (stacked on #455 · PLAN T243–T247)

The authoring layer — you can name your station's hours before anything airs differently:

• 🗓️ Schedule show assignment (T243): POST /api/schedule/assign-show — transactional run-span (single SELECT snapshot, UPDATE … RETURNING honesty, response carries the fresh week fingerprint); ScheduleSegment.ShowId is the write-authoritative field (Show stays the load projection, duality pinned); the grid PUT round-trips showId end-to-end (wire + serializer + jest — the gh-schedule: a block spanning the whole week fails to save #255 wipe-on-repaint class killed at three layers); fingerprint hashes ShowId (rename never 409s an editor). Ruling recorded: music-only runs SPAN (Dean 2026-08-10) — one click names the overnight stretch.
• 📺 Shows page (T244): list/create/edit with 60/120/400 budget maxlengths + counters, provenance line, guarded-delete rendering the block-naming 409; nav entry beside Schedule; zero coverage nudges (F119.3).
• 🎚️ Grid side-panel picker (T245): server-owned run computation (client sends only the clicked block id); union-typed target/shows states — the armed-while-unloaded window is structurally unrepresentable; narrow-mode auto-disables on runs merging >1 stored row; roster server-loaded once, projected to {id,name,tagline} (flavor never enters client state).
• 🎙️ Imaging show scope (T246): kind-agnostic write seam; station_id-gated picker (RATIFIED Dean 2026-08-10); Scope column with honest orphan label; TOCTOU window documented.
• 🔌 T247 wire, orchestrator-run on a real stack (Kestrel + Next dev + Postgres + Playwright): created "Night Moves" through the page, run-span assigned onto a merged two-stored-row music-only run — both rows landed, the Monday block held the day boundary, narrow-disable rendered. The wire caught a real bug: server re-syncs ran the merge-reconciliation over freshly-loaded overrides, so merged named runs displayed "Current: None" (write correct, display wrong, jest green) — fixed + regression-pinned through the real derivation (1457efb).

✅ Gates

Every task opus-review-gated (T243 ×3 rounds, T244 first-round PASS, T245 ×2, T246 ×2, wire-fix ×1 — all catches probe- or stash-proven). Suites: solution non-Integration 0 failed, MediaLibrary Integration 668/0, jest 99 suites/931/0, tsc clean, Architecture 95/95, -warnaserror 0/0.

🖐️ Live checklist for the pinned deploy (the T229/T233 pattern — the on-air half)

• Assign a show to a block covering now → next airing's booth rows carry show_id (query: select kind, segment_kind, show_id from station.booth_log order by id desc limit 10)
• Showless hours stamp NULL (unchanged sound everywhere — no shows configured = byte-identical station)