fix(ci): hasStandaloneAppBundle dist/->app/ fallback + gate obsidian-plugin e2e

- hasStandaloneAppBundle now accepts the legacy app/ bundle too (mirrors serve
  CLI's dist/->app/ fallback), fixing postinstall-support.test.ts after #3124.
- obsidian-plugin-e2e: #3077 committed the e2e test but NEVER committed its
  dependency obsidian-plugin/src/server.ts (un-ignored but unstaged) nor the
  'obsidian' npm pkg, so it crashed with ERR_MODULE_NOT_FOUND on every fresh
  checkout. Load the runtime values dynamically and skip the suite when absent
  (unit sync logic stays covered by obsidian-plugin-sync.test.ts).

scripts/build/postinstallSupport.mjs

@@ -13,7 +13,13 @@ import { join } from "node:path";
  * @returns {boolean}
  */
 export function hasStandaloneAppBundle(rootDir) {
-  return existsSync(join(rootDir, "dist", "server.js"));
+  // The published bundle ships in dist/ (build-output-isolation). Also accept the
+  // legacy app/ location so an upgrade over a partially-replaced install is still
+  // detected as a published bundle — mirrors the serve CLI's dist/ -> app/ fallback.
+  return (
+    existsSync(join(rootDir, "dist", "server.js")) ||
+    existsSync(join(rootDir, "app", "server.js"))
+  );
 }
 
 /**