Service: job event stream, async in-memory backend, preview routes

Ported from PR #15 (packages-side surface only; the fork's dev UI page is
intentionally dropped - the API surface is the product):
- job_events table + repository, worker emits stage transitions, additive
  GET /v1/clones/:id/events polling route. The fork's hand-written
  migration was never registered in Drizzle's journal (it silently never
  applied); regenerated properly via drizzle-kit from schema.ts with the
  (job_id, seq) index declared, and verified against a live Postgres
- In-memory backend moves to the documented enqueue-202 + poll contract
  with single-flight BUSY guard; POST honors backend httpStatus
- app-preview static serving routes; the preview BUILD half is deferred
  until the compiler exports buildApp/DEFAULT_HARNESS_DIR - routes 404
  cleanly until then
- preview option threaded through core types; cache key intentionally
  unchanged while the flag is inert

All workspaces typecheck; api 18/18, core 13/13, worker 1/1 pass;
migration verified applying (table + index + FK) on postgres:16.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/core/src/options.ts

@@ -9,6 +9,7 @@ export type ResolvedCloneOptions = CloneOptions & {
   interactions: boolean;
   components: boolean;
   motion: boolean;
+  preview: boolean;
 };
 
 export function resolveCloneMode(options: CloneOptions = {}): CloneMode {
@@ -53,5 +54,8 @@ export function resolveCloneOptions(options: CloneOptions = {}): ResolvedCloneOp
     interactions: options.interactions ?? true,
     components: options.components ?? true,
     motion: options.motion ?? true,
+    // Preview builds are the single-page product surface; multi-page exports can be
+    // large, so previewing a site clone stays an explicit opt-in.
+    preview: options.preview ?? mode === "single",
   };
 }