fix: migration 033 idempotency & smoke test cleanup (#365)

* fix(core): add IF NOT EXISTS to migration 033 index creation

The schema registry's createContentTable() creates composite indexes
on content tables at creation time. When migration 033 runs on a
database where tables were created after the registry added these
indexes, it fails with "index already exists". Adding IF NOT EXISTS
makes the migration idempotent.

* refactor(smoke): trim site matrix to templates + playground, remove typechecks

The smoke test matrix included every demo and template, plus typecheck
cases. This was slow and redundant — typechecks are already covered by
pnpm typecheck, and demos are dev targets not release artifacts.

Trim to templates + playground only, and replace the sequential per-site
astro build with a single recursive pnpm build. Remove the TypecheckSiteCase
type and handling since smoke tests should only verify runtime behavior.

* Update env

* chore: add changeset for migration 033 fix

templates/marketing/emdash-env.d.ts

@@ -17,23 +17,8 @@ export interface Page {
   bylines?: ContentBylineCredit[];
 }
 
-export interface Post {
-  id: string;
-  slug: string | null;
-  status: string;
-  title: string;
-  featured_image?: { id: string; src?: string; alt?: string; width?: number; height?: number };
-  content?: PortableTextBlock[];
-  excerpt?: string;
-  createdAt: Date;
-  updatedAt: Date;
-  publishedAt: Date | null;
-  bylines?: ContentBylineCredit[];
-}
-
 declare module "emdash" {
   interface EmDashCollections {
     pages: Page;
-    posts: Post;
   }
 }