fix(examples): merge circuitExamples via array spread, not side-effect push

Previously examples.ts pushed to exampleProjects[] after declaration, which
some bundlers can treat as dead code under aggressive tree-shaking. This
also made HMR unreliable when examples-circuits.ts changed.

Now:
  const legacyExamples = [...]
  export const exampleProjects = [...legacyExamples, ...circuitExamples]

Single immutable export. Guaranteed to include all 150 examples at import
time. The gallery (ExamplesGallery.tsx) and SSR prerender (entry-server.tsx)
both pick up the new circuit examples automatically.

Also adds frontend/src/__tests__/examples-circuits.test.ts with 5 assertions
to catch future regressions (all circuit ids present, no duplicates, valid
required fields, expected categories covered).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/__tests__/examples-circuits.test.ts

@@ -0,0 +1,45 @@
+/**
+ * Ensures that circuitExamples (examples-circuits.ts) are merged into
+ * exampleProjects so the /examples gallery and SSR prerender include them.
+ */
+import { describe, it, expect } from 'vitest';
+import { exampleProjects } from '../data/examples';
+import { circuitExamples } from '../data/examples-circuits';
+
+describe('circuitExamples integration', () => {
+  it('circuitExamples has at least 30 new examples', () => {
+    expect(circuitExamples.length).toBeGreaterThanOrEqual(30);
+  });
+
+  it('every circuitExample id appears in exampleProjects', () => {
+    const allIds = new Set(exampleProjects.map((e) => e.id));
+    const missing = circuitExamples.map((e) => e.id).filter((id) => !allIds.has(id));
+    expect(missing).toEqual([]);
+  });
+
+  it('no duplicate ids in exampleProjects', () => {
+    const ids = exampleProjects.map((e) => e.id);
+    const dupes = ids.filter((id, i) => ids.indexOf(id) !== i);
+    expect(dupes).toEqual([]);
+  });
+
+  it('circuit examples cover all expected categories', () => {
+    const cats = new Set(circuitExamples.map((e) => e.category));
+    expect(cats.has('basics')).toBe(true);
+    expect(cats.has('sensors')).toBe(true);
+    expect(cats.has('robotics')).toBe(true);
+  });
+
+  it('every example has valid required fields', () => {
+    for (const e of circuitExamples) {
+      expect(e.id, `missing id: ${JSON.stringify(e)}`).toBeTypeOf('string');
+      expect(e.title).toBeTypeOf('string');
+      expect(e.description).toBeTypeOf('string');
+      expect(e.category).toMatch(/^(basics|sensors|displays|communication|games|robotics)$/);
+      expect(e.difficulty).toMatch(/^(beginner|intermediate|advanced)$/);
+      expect(e.code).toBeTypeOf('string');
+      expect(Array.isArray(e.components)).toBe(true);
+      expect(Array.isArray(e.wires)).toBe(true);
+    }
+  });
+});

frontend/src/data/examples.ts

@@ -4,6 +4,8 @@
  * Collection of example projects that users can load and run
  */
 
+import { circuitExamples } from './examples-circuits';
+
 /** Per-board setup for multi-board examples */
 export interface ExampleBoard {
   /** Must match a BoardKind — determines the board instance ID (first board of a kind → boardKind string) */
@@ -52,7 +54,7 @@ export interface ExampleProject {
   libraries?: string[];
 }
 
-export const exampleProjects: ExampleProject[] = [
+const legacyExamples: ExampleProject[] = [
   {
     id: 'blink-led',
     title: 'Blink LED',
@@ -4799,9 +4801,10 @@ void loop() {
   },
 ];
 
-// Append circuit-focused examples (analog, digital gates, electromechanical)
-import { circuitExamples } from './examples-circuits';
-exampleProjects.push(...circuitExamples);
+// Merge legacy examples with circuit-focused examples (analog, digital gates,
+// electromechanical). Declared after both arrays exist so the export is a
+// single immutable value — safe from tree-shaking quirks.
+export const exampleProjects: ExampleProject[] = [...legacyExamples, ...circuitExamples];
 
 // Get examples by category
 export function getExamplesByCategory(category: ExampleProject['category']): ExampleProject[] {