feat(website): asciinema cast pipeline + landing quickstart demo

Settle the cast toolchain (STYLE.md #9) and build the demo pipeline end to
end. Driver: autocast, chosen by spike — its !Interactive feeds keys to the
running TUI and captures the redraw, the right model for a full-screen
crossterm app. asciinema-automation was rejected (assumes shell echo/\n Enter;
produced a garbled cast against the TUI).

- add asciinema-player; Cast.astro (player island) + Demo.astro (the WASM-swap
  seam, ADR-website-001 §3)
- casts-src/: human-readable command-lists (casts.mjs) + generate.mjs, exposed
  as `pnpm casts`; expands steps to autocast YAML and records to public/casts/.
  Command-lists are the durable source; .cast files are regenerable (final
  re-record sweep due once the app is locked).
- quickstart.cast (create -> add columns -> insert -> show data) embedded on
  the landing page above the feature cards.

Verified: pnpm build clean (25 pages); player + cast bundled and served;
landing HTML references the cast. Visual playback check pending (no headless
browser here — verify via dev server over the tunnel).

website/STYLE.md

@@ -131,15 +131,31 @@ Relationships: `books.author_id → authors.author_id` (1:n); `loans` joins
 `books` and `members` (the m:n bridge). Show `shortid` on the Types page via
 a small standalone example, not by complicating this schema.
 
-## asciinema casts  [DECIDED, details OPEN]
+## asciinema casts  [DECIDED]
 
 - Casts show *flow/motion*; static code blocks show *exact input/output*.
   Prefer a code block when a still example suffices.
 - Pair a hero/landing cast with a text transcript or the equivalent docs
   snippet (accessibility + SEO).
-- Recorded via a scripted-input driver for paced, re-recordable sessions
-  (ADR-website-001 §2; recipe in `README.md`). **[OPEN]**: cast file naming,
-  fixed terminal size, light/dark theme handling.
+- **Driver: `autocast`** (ADR-website-001 §2; chosen by the 2026-06-10
+  spike). `autocast`'s `!Interactive` feeds keys to the running TUI and
+  captures the redraw — the correct model for a full-screen crossterm app.
+  `asciinema-automation` was rejected: it assumes *shell* semantics (Enter as
+  `\n`, and an `expect()` echo-check per keystroke), which a redrawing TUI
+  breaks — it produced a garbled cast.
+- **Authoring workflow.** Source command-lists live in `casts-src/casts.mjs`
+  (human-readable steps: `type` / `wait` / `key`). `pnpm casts` runs
+  `casts-src/generate.mjs`, which expands them to autocast YAML (one key per
+  character; Enter = `^M`) and records to `public/casts/<name>.cast`. The
+  command-lists are the durable source; **`.cast` files are regenerable** —
+  re-run `pnpm casts` to re-record as the app evolves (a final sweep is due
+  once the app is locked). Needs a `cargo build` binary at `../target/debug`.
+- **Embedding.** `Demo.astro` (the WASM-swap seam, ADR-website-001 §3) wraps
+  `Cast.astro` (asciinema-player island). Call sites use `Demo`.
+- **Conventions.** Terminal geometry per cast (default 90×26); file name =
+  cast `name`; player theme `asciinema` for now. **[OPEN]**: light/dark player
+  theme sync with the Starlight theme toggle (player theme is currently fixed;
+  refine in Phase B).
 
 ## Formatting  [DECIDED, refine]
 
@@ -156,6 +172,13 @@ a small standalone example, not by complicating this schema.
 Decide these as we write; record the outcome (and escalate to an ADR if
 significant).
 
+**Resolved (2026-06-10):**
+9. ~~Cast scripting toolchain~~ → **`autocast`**, proven by spike over
+   `asciinema-automation` (which can't drive a full-screen TUI). Source
+   command-lists in `casts-src/`, `pnpm casts` to record. See the *asciinema
+   casts* section above. (Remaining sub-item: light/dark player theme sync —
+   folded into #8 / Phase B.)
+
 **Resolved (2026-06-05):**
 1. ~~Depth / organising spine~~ → **Pragmatic** four-section split (see
    Structure above).
@@ -172,7 +195,5 @@ significant).
 7. **Versioning.** Version selectors at/after v1, or single-version for
    launch? (Leaning single-version for launch.)
 8. **SEO/meta conventions.** Title/description patterns, Open Graph — settle
-   with Phase B (landing) and the `site` URL.
-9. **Cast scripting toolchain.** Confirm the scripted-input driver
-   (`asciinema-automation`/autocast vs alternative) via a test run; define
-   the `.cast` script format + storage location. (Execution task, in flight.)
+   with Phase B (landing) and the `site` URL. Also: light/dark player-theme
+   sync for embedded casts.