feat(knowledge): Phase B+C 文档提取器 + multipart 文件上传

- PDF 提取 (pdf-extract) + DOCX 提取 (zip+quick-xml) + Excel 解析 (calamine)
- 统一格式路由 detect_format() → RAG 通道或结构化通道
- POST /api/v1/knowledge/upload multipart 文件上传
- PDF/DOCX/Markdown → RAG 管线，Excel → structured_rows JSONB
- 结构化数据源 CRUD API (GET/DELETE /api/v1/structured/sources)
- POST /api/v1/structured/query JSONB 关键词查询
- 修复 industry/service.rs SaasError::Database 类型不匹配

crates/zclaw-saas/Cargo.toml

@@ -53,5 +53,11 @@ bytes = { workspace = true }
 async-stream = { workspace = true }
 genpdf = "0.2"
 
+# Document processing
+pdf-extract = { workspace = true }
+calamine = { workspace = true }
+quick-xml = { workspace = true }
+zip = { workspace = true }
+
 [dev-dependencies]
 tempfile = { workspace = true }