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>

modules/webrender/render.go

@@ -0,0 +1,71 @@
+package webrender
+
+import (
+	"fmt"
+	"html/template"
+	"io"
+	"net/url"
+	"strconv"
+	"sync"
+
+	apptemplates "git.iioio.com/freefire/jiang13-forum/templates"
+)
+
+var (
+	loadOnce sync.Once
+	tpl      *template.Template
+	loadErr  error
+)
+
+func funcMap() template.FuncMap {
+	return template.FuncMap{
+		"sortURL": func(boardID uint, sort string) string {
+			q := url.Values{}
+			if sort != "" && sort != "latest" {
+				q.Set("sort", sort)
+			}
+			path := "/"
+			if boardID > 0 {
+				path = fmt.Sprintf("/board/%d", boardID)
+			}
+			if enc := q.Encode(); enc != "" {
+				return path + "?" + enc
+			}
+			return path
+		},
+		"pageURL": func(boardID uint, sort string, page int) string {
+			q := url.Values{}
+			if sort != "" && sort != "latest" {
+				q.Set("sort", sort)
+			}
+			if page > 1 {
+				q.Set("page", strconv.Itoa(page))
+			}
+			path := "/"
+			if boardID > 0 {
+				path = fmt.Sprintf("/board/%d", boardID)
+			}
+			if enc := q.Encode(); enc != "" {
+				return path + "?" + enc
+			}
+			return path
+		},
+	}
+}
+
+// Load 解析全部模板（进程内一次）
+func Load() (*template.Template, error) {
+	loadOnce.Do(func() {
+		tpl, loadErr = template.New("root").Funcs(funcMap()).ParseFS(apptemplates.FS, "*.tmpl")
+	})
+	return tpl, loadErr
+}
+
+// Execute 渲染命名模板到 w
+func Execute(w io.Writer, name string, data any) error {
+	t, err := Load()
+	if err != nil {
+		return err
+	}
+	return t.ExecuteTemplate(w, name, data)
+}