内容结构化改造（阶段 1）：新增 topics/scenarios 目录、内容规范、frontmatter schema、校验与目录生成脚本、31 个技术栈首页骨架，周文件加 frontmatter

schema/frontmatter.schema.json

@@ -0,0 +1,25 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "zhuangang/frontmatter.schema.json",
+  "title": "zhuangang 内容文件的 frontmatter",
+  "description": "plan/、topics/、scenarios/ 下每个 .md 文件开头的 YAML frontmatter。说明见 CONTRIBUTING.md。",
+  "type": "object",
+  "required": ["id", "title", "type", "domain"],
+  "properties": {
+    "id": {"type": "string", "pattern": "^[a-z0-9]+(\\.[a-z0-9-]+)+$", "description": "全局唯一、稳定不变的内容 ID"},
+    "title": {"type": "string"},
+    "type": {"enum": ["index", "lesson", "scenario", "interview", "project", "week"]},
+    "domain": {"enum": ["backend", "devops", "python", "ai", "frontend", "cross", "plan"]},
+    "stack": {"type": "array", "items": {"type": "string"}, "description": "技术栈标识，与 topics/<domain>/<stack>/ 目录名一致"},
+    "tags": {"type": "array", "items": {"type": "string"}},
+    "level": {"enum": ["basic", "intermediate", "advanced"]},
+    "prerequisites": {"type": "array", "items": {"type": "string"}, "description": "先修内容的 id"},
+    "related": {"type": "array", "items": {"type": "string"}, "description": "相关内容的 id"},
+    "est_hours": {"type": "number", "minimum": 0},
+    "week": {"type": "array", "items": {"type": "integer", "minimum": 1, "maximum": 16}, "description": "在 16 周计划中的哪几周用到"},
+    "order": {"type": "integer", "description": "同一技术栈内的排序"}
+  },
+  "allOf": [
+    {"if": {"properties": {"type": {"enum": ["lesson", "scenario", "interview"]}}}, "then": {"required": ["level", "stack"]}}
+  ]
+}