feat(website): projects cast (vi-nav load picker) + --demo on all casts

- New projects cast: create → save as library → new (fresh) → load → navigate
  the picker to the saved project (j, now possible via #24 vi-nav) → Enter
  loads it, the table is restored. Runs under an isolated --data-dir so the
  picker lists only this cast's projects.
- Turn on the demonstration overlay (--demo, #22 / ADR-0047) for ALL casts,
  for a consistent viewer experience: special keys show a badge — e.g.
  [ENTER], and [TAB] at the assistive-editor's completion moment, finally
  making that keystroke visible. Plain j/k navigation stays unbadged, so the
  picker navigation is not surfaced.
- Generator: per-cast `dataDir` (isolated data root) + default-on `--demo`
  (opt out with demo:false). All 7 casts regenerated.

Convert projects.md → .mdx and embed. Build clean (26 pages). Visual playback
of all casts pending a tunnel check.

website/casts-src/casts.mjs

@@ -19,6 +19,28 @@
 
 /** The shared library narrative, trimmed per cast. */
 export const casts = [
+  {
+    name: 'projects',
+    title: 'Save a project, start fresh, then load it back',
+    width: 90,
+    height: 26,
+    typeSpeed: '45ms',
+    dataDir: true, // isolated data root → picker lists only this cast's projects
+    steps: [
+      { wait: 1000 },
+      { type: 'create table books with pk', after: 600 },
+      { type: 'add column to books: title (text)', after: 700 },
+      { type: "insert into books (title) values ('A Wizard of Earthsea')", after: 700 },
+      { type: 'show data books', after: 1500 }, // a saved project with content
+      { type: 'save as', after: 900 }, // opens the name prompt
+      { type: 'library', enter: true, after: 1500 }, // name it → saved as "library"
+      { type: 'new', after: 1500 }, // start fresh — the table is gone
+      { type: 'load', after: 1200 }, // opens the project picker
+      { type: 'j', enter: false, after: 1000 }, // move the selection to "library"
+      { key: 'Enter', after: 2000 }, // load it — the table is back
+      { key: 'CtrlC' }, // quit invisibly (Ctrl-C) — cast ends on the last content frame
+    ],
+  },
   {
     name: 'modes',
     title: 'Simple mode, then advanced — with the SQL the playground runs for you',

website/casts-src/generate.mjs

@@ -110,10 +110,18 @@ function trimCast(outPath, { holdEnd = 1.5 } = {}) {
   );
 }
 
-function yamlFor(cast) {
+function yamlFor(cast, dataDir) {
   const keys = keysFor(cast.steps)
     .map((k) => `      - ${k}`)
     .join('\n');
+  // Build the launch command. `--demo` turns on the demonstration overlay
+  // (ADR-0047): automatic keystroke badges (so otherwise-invisible keys like
+  // `j` / Tab / Enter are shown) plus `Ctrl+]`-delimited step captions.
+  // `--data-dir` isolates the recording from the user's real projects (and
+  // keeps the load picker listing only this cast's projects).
+  const cmd = ['rdbms-playground'];
+  if (cast.demo !== false) cmd.push('--demo'); // on for all casts (opt out with demo:false)
+  if (dataDir) cmd.push('--data-dir', dataDir);
   return [
     'settings:',
     `  width: ${cast.width ?? 90}`,
@@ -124,7 +132,7 @@ function yamlFor(cast) {
     '  prompt: "$ "',
     'instructions:',
     '  - !Interactive',
-    '    command: rdbms-playground',
+    `    command: ${cmd.join(' ')}`,
     '    keys:',
     keys,
     '',
@@ -145,7 +153,16 @@ let failures = 0;
 for (const cast of selected) {
   const yamlPath = resolve(os.tmpdir(), `autocast-${cast.name}.yaml`);
   const outPath = resolve(outDir, `${cast.name}.cast`);
-  writeFileSync(yamlPath, yamlFor(cast));
+  // Per-cast isolated data root (so the load picker lists only this cast's
+  // projects and nothing touches the user's real data dir). Wiped fresh each
+  // run for a deterministic picker order.
+  let dataDir = null;
+  if (cast.dataDir) {
+    dataDir = resolve(os.tmpdir(), `rdbms-cast-data-${cast.name}`);
+    rmSync(dataDir, { recursive: true, force: true });
+    mkdirSync(dataDir, { recursive: true });
+  }
+  writeFileSync(yamlPath, yamlFor(cast, dataDir));
   console.log(`▶ recording ${cast.name} → public/casts/${cast.name}.cast`);
   const res = spawnSync('autocast', ['--overwrite', yamlPath, outPath], {
     env,