feat: show kind infra — schemas, budget lint, golden fixture, four-kinds docs

[genwave-radio]

🎙️ The show kind's machinery (Dayparting epic · app-side SPEC F118 · STORY-314)

Infra-only (zero entries/ — diff-scope guard green). Stacked structure per the theme/font precedent: this PR = machinery; the 12 seed show entries follow in their own PR.

• Schemas: show-manifest.schema.json (<slug>.show.json: schemaVersion/name/tagline/flavor — types-only, budgets live in the lint per F89.5) + show-meta.schema.json (audience required; optional bestFor[]; optional suggestedPersona — slug-pattern-pinned + 64-char cap matching the app's BoundedImportBodyReader, never projected into index.json).
• Lint: name 60 / tagline 120 / flavor 400 — WARN past 1×, HARD red at ≥2× (deliberately one char stricter than the app parser's >2×; documented both sides).
• fixtures/golden.show.json: the cross-repo parity fixture (the app repo pins the same bytes — T254).
• Selftest: 99 checks / 0 fail — red-proofs incl. exact-2× flavor, missing audience, hostile suggestedPersona (traversal/URL/script/newline/65-char), stowaway asset, index cross-dressing.
• Docs: README/CONTRIBUTING/PR template all speak four kinds; new 🎙 Show submission section (shows are open to community per the standing ruling — font packs remain the only Dean-curated-only kind).

Review-gated ×3 rounds (opus): suggestedPersona was unconstrained on round 1 — now pattern+length-pinned with mutation-proof fixtures; six stale kind enumerations swept; the maxLength mutant killed.

Merge when ready — the seed-entries PR (one show per demo DJ, suggestedPersona wired) lands on top.