docs(website): hint feature docs + cast (content for c84a640)

Completes the preceding empty-rename commit: the getting-help "Hints"
section — F1 for a tier-3 teaching hint on the live input, `hint` to
explain the most recent error — with the real rendered block and a cast
showing both (the live-input hint via the demo-mode Ctrl-G→[F1] alias,
since autocast can't send F1, then `hint` on an error). the-assistive-editor
points at F1; CtrlG added to the cast generator's key map.

website/casts-src/generate.mjs

@@ -49,6 +49,11 @@ const NAMED_KEYS = {
   CtrlO: '^O',
   // Esc leaves navigation mode directly (back to the input field).
   Esc: '^[',
+  // Ctrl-G: in demo mode the app aliases this to F1 (the contextual-hint key,
+  // ADR-0053) and badges it AS [F1] (ADR-0047 Amendment 1). autocast can't emit
+  // F1 (an escape sequence), but it can send this single control byte — so a
+  // cast can show the live-input hint exactly as a real F1 press would.
+  CtrlG: '^G',
 };
 
 /** Build the autocast `keys:` list (one entry per line) for a cast's steps. */