开源准备：重写 README 展示 UI/UX，更新模块路径

- 新增界面截图与 CONTRIBUTING.md
- README 以三栏布局、暗色主题、移动端等视觉亮点为主
- go module 迁移至 git.iioio.com/freefire/jiang13-forum

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/capture-screenshots.mjs

@@ -0,0 +1,86 @@
+import { chromium } from 'playwright';
+import { mkdir } from 'node:fs/promises';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const outDir = path.join(__dirname, '..', 'docs', 'screenshots');
+const base = process.env.J13_URL || 'http://localhost:8080';
+
+async function shot(page, name, opts = {}) {
+  const file = path.join(outDir, name);
+  await page.screenshot({ path: file, type: 'png', ...opts });
+  console.log('saved', file);
+}
+
+async function setTheme(page, theme) {
+  await page.addInitScript((t) => {
+    localStorage.setItem('j13-theme', t);
+    document.documentElement.classList.toggle('dark', t === 'dark');
+    document.documentElement.style.colorScheme = t;
+  }, theme);
+}
+
+const browser = await chromium.launch();
+const context = await browser.newContext({ deviceScaleFactor: 2 });
+
+try {
+  await mkdir(outDir, { recursive: true });
+
+  // 首页 · 浅色
+  {
+    const page = await context.newPage();
+    await page.setViewportSize({ width: 1440, height: 900 });
+    await setTheme(page, 'light');
+    await page.goto(`${base}/`, { waitUntil: 'networkidle' });
+    await page.waitForTimeout(800);
+    await shot(page, 'home-light.png');
+    await page.close();
+  }
+
+  // 首页 · 暗色
+  {
+    const page = await context.newPage();
+    await page.setViewportSize({ width: 1440, height: 900 });
+    await setTheme(page, 'dark');
+    await page.goto(`${base}/`, { waitUntil: 'networkidle' });
+    await page.waitForTimeout(800);
+    await shot(page, 'home-dark.png');
+    await page.close();
+  }
+
+  // 帖子详情
+  {
+    const page = await context.newPage();
+    await page.setViewportSize({ width: 1440, height: 900 });
+    await setTheme(page, 'light');
+    await page.goto(`${base}/post/2`, { waitUntil: 'networkidle' });
+    await page.waitForTimeout(1000);
+    await shot(page, 'post-detail.png');
+    await page.close();
+  }
+
+  // 发帖编辑器
+  {
+    const page = await context.newPage();
+    await page.setViewportSize({ width: 1440, height: 900 });
+    await setTheme(page, 'light');
+    await page.goto(`${base}/compose`, { waitUntil: 'networkidle' });
+    await page.waitForTimeout(800);
+    await shot(page, 'compose.png');
+    await page.close();
+  }
+
+  // 移动端
+  {
+    const page = await context.newPage();
+    await page.setViewportSize({ width: 390, height: 844 });
+    await setTheme(page, 'light');
+    await page.goto(`${base}/`, { waitUntil: 'networkidle' });
+    await page.waitForTimeout(800);
+    await shot(page, 'mobile-home.png', { fullPage: true });
+    await page.close();
+  }
+} finally {
+  await browser.close();
+}