feat(website): sql-echo cast — the DSL→SQL teaching echo demo

Advanced-mode cast running simple commands (create table, add column),
culminating in `create m:n relationship` expanding to a full junction
table, each tagged `Executing SQL:`. Recorded at height 34 so the long
m:n echo + junction structure stay fully on screen. Verified against
real app output.

website/casts-src/casts.mjs

@@ -48,6 +48,33 @@ export const casts = [
       { key: 'CtrlC' }, // quit invisibly (Ctrl-C) — cast ends on the last content frame
     ],
   },
+  {
+    name: 'sql-echo',
+    title: 'Run simple-mode commands in advanced mode and watch the SQL they map to',
+    width: 90,
+    // Taller than the other casts (26): the m:n command's echo + the junction
+    // structure it prints are long, and at 26 rows the head of the `Executing
+    // SQL:` echo — the payoff — scrolled off the top. The extra rows all go to
+    // the output pane (the surrounding panels are fixed-height), keeping the
+    // whole echo visible. Stays < 40 so the compact 1-row-input layout holds.
+    height: 34,
+    typeSpeed: '45ms',
+    steps: [
+      { wait: 1000 },
+      { type: 'mode advanced', after: 1300 },
+      // Each simple-mode command, run in advanced mode, echoes the equivalent
+      // SQL beneath it (the ADR-0038 teaching echo).
+      { type: 'create table books with pk', after: 1700 },
+      { type: 'add column to books: title (text)', after: 1800 },
+      { type: 'create table tags with pk', after: 1600 },
+      { type: 'add column to tags: label (text)', after: 1900 },
+      // The crescendo: one m:n command expands to a whole junction table —
+      // split type + Enter so the command reads before the long echo lands.
+      { type: 'create m:n relationship from books to tags', enter: false, after: 1700 },
+      { key: 'Enter', after: 3200 },
+      { key: 'CtrlC' }, // quit invisibly (Ctrl-C) — cast ends on the last content frame
+    ],
+  },
   {
     name: 'projects',
     title: 'Save a project, start fresh, then load it back',