fix(content-gen): strip URLs and site-list sections from generated content

Forbid URLs/domains/markdown links across prompt rules (runtime, platform
templates, outline/imitation/title flows) and rename "官网" placeholder to
"官网信息" with explicit instructions that links are background only.
Add sanitizeGeneratedArticleMarkdown to strip URLs, HTML images, and
"网站列表/官网列表" labels from LLM output, wired into article, prompt-rule,
template, and outline generation. Drop the site_list outline section seed
and filter blocked outline keys in the wizard so stored drafts cannot
resurrect it.

server/internal/tenant/prompts/template_seeds.go

@@ -107,7 +107,6 @@ var platformTemplateSeeds = []PlatformTemplateSeed{
       "preview_caption": "预览会根据已选标题和结构实时更新。",
       "sections": [
         { "key": "intro", "label": "引言", "default": true },
-        { "key": "site_list", "label": "网站列表", "default": true },
         { "key": "key_points", "label": "文章关键要点", "default": true },
         { "key": "what_is_question", "label_template": "围绕{{brand_question}}展开", "default": false },
         { "key": "features", "label": "特点", "default": false },