fix(brand): force visible platform-brand footer on published pages

Inject serve-time CSS so author styles cannot hide TKMind · 智趣 with
low opacity, which made pages like weather.html look brandless.

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

wechat/prompts/page-generate.mjs

@@ -28,7 +28,7 @@ export function buildPageGenerateAgentPrompt(intent, { wantsDocx = false } = {})
     '   - `<meta name="description" content="一句话摘要">`',
     '   - `<meta name="mindspace-cover" content=\'{"tag":"主题","accent":"#主色","accent2":"#辅色","subtitle":"卖点","cover":"assets/hero.jpg"}\'>`',
     '   tag/accent/subtitle 必须与页面主题一致；有 hero 图时 cover 指向同目录 raster 图（jpg/png）。',
-    '6. 页脚加 `<p data-mindspace-page-tag="platform-brand">TKMind · 智趣</p>`（必须，禁止省略或用邮箱/tkmind.ai 代替）。',
+    '6. 页脚加 `<p data-mindspace-page-tag="platform-brand">TKMind · 智趣</p>`（必须；禁止省略、不要用邮箱/tkmind.ai，也不要把该行 opacity 设太低导致看不见）。',
     '7. 回复里只给一个正式域名链接；没有落盘或缺少上述元数据就不要发链接。',
     '',
     buildCurrentTimeAgentPrefix({ timezone: scheduleTimezone }),