fix(admin): 主题设置集合结构修复 + 集合结构构建校验

用户实测后台报错：「主题设置 集合: The file option content/site/theme.yaml is
invalid. It must be the path to a JSON file」——根因是 site_theme 把 `file:`
直接写在集合层级，而 Decap/Sveltia 的文件集合必须是
`files: [{ name, label, file, format, fields }]` 结构；缺 files 包装时 Sveltia
按单文件变体解析并期待 JSON 路径，故报该错。

- site_theme 改为标准 files 集合（format: yaml 显式声明）
- site_pages 三单例补显式 format: yaml（扩展名推断可用但显式更稳）
- config-check.py 增加结构断言：每个集合必须 folder 或 files 二选一、files
  项必须齐 file/label/fields、file 必须指向真实文件——这类"后台整体打不开"
  的结构错从此在构建期拦截

验证: config-check 五文件全 OK（207 字段/64 hint）+ 结构断言通过；
      pnpm astro build exit 0

Spec: none (后台配置结构修复，构建校验加固)

Co-authored-by: GLM-5.3

public/admin/config.yml

@@ -61,28 +61,33 @@ collections:
   # 主题旋钮（样式即数据 · 层 4）：只放白名单内的 9 组，越界值会被构建期钳制
   - name: site_theme
     label: 主题设置
-    file: content/site/theme.yaml
-    fields:
-      - { label: 强调色（亮）, name: accent_light, widget: color, required: false, hint: '亮色模式强调色，如 #3454d1；构建期校验正文对比度 ≥4.5' }
-      - { label: 强调色（暗）, name: accent_dark, widget: color, required: false, hint: '暗色模式强调色，如 #8ea2ff' }
-      - { label: 图片圆角, name: radius_img, widget: number, required: false, value_type: int, min: 4, max: 16, hint: '范围 4–16（建议 ≤14）' }
-      - { label: 一级标题字号, name: text_h1, widget: number, required: false, value_type: int, min: 22, max: 32, hint: '22–32，且必须大于 h2' }
-      - { label: 二级标题字号, name: text_h2, widget: number, required: false, value_type: int, min: 22, max: 32, hint: '22–32，必须小于 h1、大于 h3' }
-      - { label: 三级标题字号, name: text_h3, widget: number, required: false, value_type: int, min: 16, max: 32, hint: '16–32，必须小于 h2' }
-      - { label: 书评正文字号, name: prose_size_reading, widget: number, required: false, value_type: int, min: 16, max: 22, hint: '16–22' }
-      - { label: 技术文正文字号, name: prose_size_tech, widget: number, required: false, value_type: int, min: 16, max: 22, hint: '16–22' }
-      - { label: 书评行高, name: leading_reading, widget: number, required: false, value_type: float, min: 1.5, max: 2.0, step: 0.05, hint: '1.5–2.0' }
-      - { label: 技术文行高, name: leading_tech, widget: number, required: false, value_type: float, min: 1.5, max: 2.0, step: 0.05, hint: '1.5–2.0' }
-      - { label: 间距 3, name: space_3, widget: number, required: false, value_type: int, min: 8, max: 80, hint: '8–80，必须 < 间距 4' }
-      - { label: 间距 4, name: space_4, widget: number, required: false, value_type: int, min: 8, max: 80, hint: '8–80，必须 > 间距 3 且 < 间距 5' }
-      - { label: 间距 5, name: space_5, widget: number, required: false, value_type: int, min: 8, max: 80, hint: '8–80，必须 > 间距 4 且 < 间距 6' }
-      - { label: 间距 6, name: space_6, widget: number, required: false, value_type: int, min: 8, max: 80, hint: '8–80，必须 > 间距 5' }
-      - { label: 段间距, name: flow_p, widget: number, required: false, value_type: float, min: 0, max: 2, step: 0.05, hint: '0–2（em）' }
-      - { label: 标题下间距, name: flow_h2_post, widget: number, required: false, value_type: float, min: 0, max: 2, step: 0.05, hint: '0–2（em）' }
-      - { label: 过渡时长, name: dur, widget: number, required: false, value_type: int, min: 150, max: 600, hint: '150–600（毫秒）' }
+    # 文件集合必须是 files: [{file,label,fields}] 结构；把 file 直接写在集合层级会被 Sveltia 判非法（2026-11-02 实测报 "The file option ... is invalid"）
+    files:
+      - name: theme
+        label: 主题设置
+        file: content/site/theme.yaml
+        format: yaml
+        fields:
+          - { label: 强调色（亮）, name: accent_light, widget: color, required: false, hint: '亮色模式强调色，如 #3454d1；构建期校验正文对比度 ≥4.5' }
+          - { label: 强调色（暗）, name: accent_dark, widget: color, required: false, hint: '暗色模式强调色，如 #8ea2ff' }
+          - { label: 图片圆角, name: radius_img, widget: number, required: false, value_type: int, min: 4, max: 16, hint: '范围 4–16（建议 ≤14）' }
+          - { label: 一级标题字号, name: text_h1, widget: number, required: false, value_type: int, min: 22, max: 32, hint: '22–32，且必须大于 h2' }
+          - { label: 二级标题字号, name: text_h2, widget: number, required: false, value_type: int, min: 22, max: 32, hint: '22–32，必须小于 h1、大于 h3' }
+          - { label: 三级标题字号, name: text_h3, widget: number, required: false, value_type: int, min: 16, max: 32, hint: '16–32，必须小于 h2' }
+          - { label: 书评正文字号, name: prose_size_reading, widget: number, required: false, value_type: int, min: 16, max: 22, hint: '16–22' }
+          - { label: 技术文正文字号, name: prose_size_tech, widget: number, required: false, value_type: int, min: 16, max: 22, hint: '16–22' }
+          - { label: 书评行高, name: leading_reading, widget: number, required: false, value_type: float, min: 1.5, max: 2.0, step: 0.05, hint: '1.5–2.0' }
+          - { label: 技术文行高, name: leading_tech, widget: number, required: false, value_type: float, min: 1.5, max: 2.0, step: 0.05, hint: '1.5–2.0' }
+          - { label: 间距 3, name: space_3, widget: number, required: false, value_type: int, min: 8, max: 80, hint: '8–80，必须 < 间距 4' }
+          - { label: 间距 4, name: space_4, widget: number, required: false, value_type: int, min: 8, max: 80, hint: '8–80，必须 > 间距 3 且 < 间距 5' }
+          - { label: 间距 5, name: space_5, widget: number, required: false, value_type: int, min: 8, max: 80, hint: '8–80，必须 > 间距 4 且 < 间距 6' }
+          - { label: 间距 6, name: space_6, widget: number, required: false, value_type: int, min: 8, max: 80, hint: '8–80，必须 > 间距 5' }
+          - { label: 段间距, name: flow_p, widget: number, required: false, value_type: float, min: 0, max: 2, step: 0.05, hint: '0–2（em）' }
+          - { label: 标题下间距, name: flow_h2_post, widget: number, required: false, value_type: float, min: 0, max: 2, step: 0.05, hint: '0–2（em）' }
+          - { label: 过渡时长, name: dur, widget: number, required: false, value_type: int, min: 150, max: 600, hint: '150–600（毫秒）' }
 
-  # 瞬间：随手发（text/image 至少其一——Sveltia 无法表达条件必填，两者都设可选，
-  # 保存前自查；pubDate 必填）。图片走图库媒体库（content/photos 同源可复用）
+      # 瞬间：随手发（text/image 至少其一——Sveltia 无法表达条件必填，两者都设可选，
+      # 保存前自查；pubDate 必填）。图片走图库媒体库（content/photos 同源可复用）
   - name: moments
     label: 瞬间
     folder: content/moments
@@ -136,6 +141,7 @@ collections:
       - name: home
         label: 主页设置
         file: content/site/home.yaml
+        format: yaml
         # 头像上传落 content/site/assets/，yaml 写 ./assets/xxx（Astro 图片管线优化）
         media_folder: content/site/assets
         public_folder: ./assets
@@ -244,6 +250,7 @@ collections:
       - name: about
         label: 关于页
         file: content/site/about.yaml
+        format: yaml
         # 块内图片上传落 content/site/assets/，yaml 写 ./assets/xxx（Astro 图片管线）
         media_folder: content/site/assets
         public_folder: ./assets
@@ -521,6 +528,7 @@ collections:
       - name: opensource
         label: 开源页
         file: content/site/opensource.yaml
+        format: yaml
         fields:
           - label: 叙述（链接前）
             name: blurb