feat(site-import): 行为骨架模板与 few-shot 语料

- template/ 四件套：system/extractor/evaluator 骨架 + placeholders.json 占位符清单
  （system 15 个占位符，固定段与 jiancai 原文逐字一致——行级来源审计 0 缺失）
- fewshot/ 语料摘录：yotaienergys/televicsic 两生产租户四件套行业化片段
  （10592 字节 ≤18000 上限），README 含来源声明与数据治理记档
- tests/test_site_import_template.py：行业残留黑名单/占位符对称/红线锚点/
  行级来源/fewshot 尺寸与用途段守卫，7 条

Co-Authored-By: Claude Code <noreply@anthropic.com>

app/platform/site_import/template/placeholders.json

@@ -0,0 +1,35 @@
+{
+  "system": [
+    "身份描述",
+    "产品类别清单",
+    "认证清单",
+    "预算数字示例",
+    "固定追问句",
+    "零上下文首轮例句",
+    "产品统称EN",
+    "推荐建议",
+    "产品统称",
+    "已知信息重问示例",
+    "规格追问三要素",
+    "产品追问示例",
+    "品类错推示例",
+    "好差示例组",
+    "关注信息"
+  ],
+  "extractor": [
+    "采购域",
+    "示例字段清单",
+    "字段说明组",
+    "外文对照例",
+    "原样保留字段"
+  ],
+  "evaluator": [
+    "采购域",
+    "意向要素",
+    "浏览对象",
+    "缺失关键信息",
+    "正例",
+    "负例",
+    "浏览例句"
+  ]
+}