chore(v028): 앱 아이콘 (assets/icon.svg → ICO/ICNS/PNG) + electron-builder config

- electron-icon-builder + sharp devDep 추가
- assets/icon.svg → build/icon.{ico,icns,png} 산출 + git 추적
- electron-icon-builder 가 SVG 직접 input 안 받음 (Jimp MIME 에러) — sharp 로 SVG → PNG 1024 변환 후 input
- scripts/svg-to-png.mjs (sharp 사용 SVG→PNG) + scripts/finalize-icons.mjs (build/icons/ → build/ 정규 위치 정리)
- package.json build.{win,mac,linux}.icon 키 추가
- .gitignore: build/icons/ 와 build/icon-source.png (중간 산출물) 무시, build/icon.* 는 추적
- typecheck 0 errors + 472/472 단위 통과 유지 (회귀 없음)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/finalize-icons.mjs

@@ -0,0 +1,35 @@
+import { copyFileSync, renameSync, existsSync } from 'node:fs';
+import { join } from 'node:path';
+
+// electron-icon-builder --flatten 은 build/icons/ 안에 icon.ico, icon.icns, <size>x<size>.png
+// 들을 만든다. electron-builder 는 build/icon.ico, build/icon.icns, build/icon.png 를
+// 기대 — 정규 위치로 옮긴다.
+const buildDir = 'build';
+const iconsDir = join(buildDir, 'icons');
+
+const moves = [
+  ['icon.ico', 'icon.ico'],
+  ['icon.icns', 'icon.icns'],
+];
+
+for (const [src, dest] of moves) {
+  const from = join(iconsDir, src);
+  const to = join(buildDir, dest);
+  if (existsSync(from)) {
+    renameSync(from, to);
+    console.log(`Moved: ${from} -> ${to}`);
+  } else {
+    console.error(`MISSING: ${from}`);
+    process.exit(1);
+  }
+}
+
+const png1024 = join(iconsDir, '1024x1024.png');
+const pngOut = join(buildDir, 'icon.png');
+if (existsSync(png1024)) {
+  copyFileSync(png1024, pngOut);
+  console.log(`Copied: ${png1024} -> ${pngOut}`);
+} else {
+  console.error(`MISSING: ${png1024}`);
+  process.exit(1);
+}

scripts/svg-to-png.mjs

@@ -0,0 +1,14 @@
+import sharp from 'sharp';
+import { readFileSync, writeFileSync, mkdirSync } from 'node:fs';
+import { dirname } from 'node:path';
+
+const [, , input, output, size = '1024'] = process.argv;
+if (!input || !output) {
+  console.error('Usage: svg-to-png.mjs <input.svg> <output.png> [size]');
+  process.exit(1);
+}
+mkdirSync(dirname(output), { recursive: true });
+const svg = readFileSync(input);
+const png = await sharp(svg).resize(Number(size), Number(size)).png().toBuffer();
+writeFileSync(output, png);
+console.log(`OK: ${output} (${size}x${size})`);