feat: Sanity CMS integration with filesystem fallback, deck rename

[developeranku]

Summary

• Add optional Sanity CMS as an authoring source. The app boots without Sanity env vars and serves filesystem decks only; with Sanity configured, decks from both sources are merged (Sanity wins on slug collision).
• Embed Sanity Studio at `/studio` with a `deck` schema (metadata + slides[] containing full HTML per slide).
• Rename `case-studies/` folder to `slides/` (gitignored, per-developer working dir).
• Rename all `caseStudy` / `CaseStudy` identifiers to `deck` / `Deck` across types, functions, schema, GROQ queries, cache tags, webhook handlers, and docs for OSS-friendly naming.
• Inject `` when serving slide HTML so relative `./assets/...` paths resolve correctly inside the iframe.
• Rewrite README end-to-end for an open-source audience (quick-start, authoring contract, meta.json reference, routes, env vars, keyboard shortcuts, deploy notes, contributing guardrails).
• Add `/api/revalidate` webhook receiver that validates Sanity HMAC signatures and refreshes affected cache tags.

Test plan

• `pnpm dev` boots without any env vars set, filesystem decks load from `slides//`.
• Drop a folder into `slides/hello/` with a `meta.json` and HTML files, reload, verify it appears on the index.
• Verify slide images load (the `` tag fix).
• Verify viewer keyboard shortcuts (1-9, F, Esc, arrows).
• Verify PDF download with the appended contact card page.
• Verify per-deck OG image renders without Satori errors.
• With Sanity env vars set, verify `/studio` loads, a published deck appears in the index alongside filesystem decks, and `/api/revalidate` is reachable.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
stackdeck	Ready	Preview, Comment	May 7, 2026 11:55am