feat: placeholder app icons (clock-with-target motif)

Generate the manifest/PWA + native-wrapper icons that were referenced but
missing (icon-192/512 were 404). A reproducible pure-Node generator
(tools/gen-icons.mjs, npm run gen:icons) draws a clock ring with amber
hands + a green target dot in the app palette — no image deps, hand-rolled
PNG encoder with analytic anti-aliasing.

- public/icons/icon-192, -512, -180 (apple-touch); linked in index.html.
- resources/icon.png (1024) + splash.png (2732) for @capacitor/assets.
- tests/tools/icons.test.js ties every manifest icon to a real PNG of the
  declared size. 213 tests pass; icons now serve 200.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/tools/icons.test.js

@@ -0,0 +1,31 @@
+import { describe, it, expect } from 'vitest';
+import { readFileSync } from 'node:fs';
+
+// PNG: 8-byte signature, then IHDR with width/height at bytes 16..24.
+function pngInfo(path) {
+  const b = readFileSync(path);
+  const isPng = b[0] === 0x89 && b[1] === 0x50 && b[2] === 0x4e && b[3] === 0x47;
+  return { isPng, width: b.readUInt32BE(16), height: b.readUInt32BE(20), bytes: b.length };
+}
+
+const manifest = JSON.parse(readFileSync('public/manifest.webmanifest', 'utf8'));
+
+describe('app icons', () => {
+  it('every manifest icon exists as a valid PNG of the declared size', () => {
+    expect(manifest.icons.length).toBeGreaterThan(0);
+    for (const icon of manifest.icons) {
+      const path = 'public' + icon.src;          // e.g. /icons/icon-192.png → public/icons/...
+      const info = pngInfo(path);
+      const [w] = icon.sizes.split('x').map(Number);
+      expect(info.isPng, path).toBe(true);
+      expect(info.width, path + ' width').toBe(w);
+      expect(info.height, path + ' height').toBe(w);
+      expect(info.bytes, path + ' non-empty').toBeGreaterThan(100);
+    }
+  });
+
+  it('ships the apple-touch icon referenced by index.html', () => {
+    expect(readFileSync('index.html', 'utf8')).toContain('/icons/icon-180.png');
+    expect(pngInfo('public/icons/icon-180.png').width).toBe(180);
+  });
+});