chore: 💄 use a realistic message for the markdown block fixture

Reframe the playground fixture as a standard deploy-summary message
instead of a "now emoji work" demo, while still exercising emoji in a
header, prose, list items, a skin tone and an alias.

https://claude.ai/code/session_01Qea1JoBqVXi6R8Fw3QWCr7

Author: claude

playground/src/fixtures.ts

@@ -207,22 +207,32 @@ export const FIXTURES: Fixture[] = [
     ],
   },
   {
-    id: "markdown-emoji",
-    label: "Markdown · emoji",
+    id: "markdown-block",
+    label: "Markdown block",
     blocks: [
       {
         type: "markdown",
         text: [
-          "Emoji now render inside `markdown` blocks, just like in `section` blocks:",
+          "## :rocket: Deploy — api v2.4.0",
           "",
-          "- Standard: :tada: :smile: :rocket:",
-          "- Aliases: :thumbsup: :hankey:",
-          "- Skin tone: :wave::skin-tone-3:",
+          "Out to production :tada: Thanks for the reviews this week :clap::skin-tone-3:",
           "",
-          "Inside code they stay literal — inline `:tada:` and fenced:",
+          "**What changed**",
           "",
-          "```",
-          ":no_entry: :tada:",
+          "- Carousel and card blocks :sparkles:",
+          "- Faster cold starts :zap:",
+          "- Dark mode contrast fixes :bug:",
+          "",
+          "**Rollout checklist**",
+          "",
+          "- [x] Migrations applied",
+          "- [x] Smoke tests passing :white_check_mark:",
+          "- [ ] Changelog updated :thumbsup:",
+          "",
+          "Roll back with `kubectl rollout undo deploy/api` if error rates spike :warning:",
+          "",
+          "```bash",
+          "curl -s https://api.example.com/healthz | jq .status",
           "```",
         ].join("\n"),
       },