feat: add PDF document recognition with 10-page pre-hook

- Migrate recognition_results table to JSON schema (meta_data + content),
  replacing flat latex/markdown/mathml/mml columns
- Add TaskTypePDF constant and update all formula read/write paths
- Add PDFRecognitionService using pdftoppm (Poppler) for CGO-free page
  rendering; limits processing to first 10 pages (pre-hook)
- Reuse existing downstream OCR endpoint (cloud.texpixel.com) for each
  page image; stores results as [{page_number, markdown}] JSON array
- Add Redis queue + distributed lock for PDF worker goroutine
- Add REST endpoints: POST /v1/pdf/recognition, GET /v1/pdf/recognition/:task_no
- Add .pdf to OSS upload file type whitelist
- Add migrations/pdf_recognition.sql for safe data migration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/router.go

@@ -4,6 +4,7 @@ import (
 	"gitea.com/texpixel/document_ai/api/v1/analytics"
 	"gitea.com/texpixel/document_ai/api/v1/formula"
 	"gitea.com/texpixel/document_ai/api/v1/oss"
+	"gitea.com/texpixel/document_ai/api/v1/pdf"
 	"gitea.com/texpixel/document_ai/api/v1/task"
 	"gitea.com/texpixel/document_ai/api/v1/user"
 	"gitea.com/texpixel/document_ai/pkg/common"
@@ -55,6 +56,13 @@ func SetupRouter(engine *gin.RouterGroup) {
 			userAuthRouter.GET("/info", common.MustAuthMiddleware(), userEndpoint.GetUserInfo)
 		}
 
+		pdfRouter := v1.Group("/pdf", common.GetAuthMiddleware())
+		{
+			endpoint := pdf.NewPDFEndpoint()
+			pdfRouter.POST("/recognition", endpoint.CreateTask)
+			pdfRouter.GET("/recognition/:task_no", endpoint.GetTaskStatus)
+		}
+
 		// 数据埋点路由
 		analyticsRouter := v1.Group("/analytics", common.GetAuthMiddleware())
 		{