docs+feat: 重构规格与 Gitea 式 SSR 骨架（首页）

在 rebuild/gitea-ssr 落地产品规格、Cursor 规则，以及 Go 模板 SSR 首页/板块列表；未迁移路径仍回落 SPA，便于对照 main。

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

web_src/build.mjs

@@ -0,0 +1,14 @@
+import { cpSync, mkdirSync, rmSync, existsSync } from "node:fs";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const root = dirname(fileURLToPath(import.meta.url));
+const outDir = join(root, "..", "public", "assets");
+
+if (existsSync(outDir)) {
+  rmSync(outDir, { recursive: true, force: true });
+}
+mkdirSync(outDir, { recursive: true });
+cpSync(join(root, "css", "site.css"), join(outDir, "site.css"));
+cpSync(join(root, "js", "site.js"), join(outDir, "site.js"));
+console.log("[web_src] built -> public/assets/");