Align Go parser backends and PDF pipeline with Python (#16676)

Ports remaining Go parser wiring and PDF backends, adds tenant-aware VLM
dispatch, aligns post-processing with Python, and adds end-to-end
pipeline coverage with a generated six-page PDF.

internal/parser/parser/pdf_parser_paddleocr.go

@@ -0,0 +1,62 @@
+package parser
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	models "ragflow/internal/entity/models"
+)
+
+func parsePDFWithPaddleOCR(filename string, data []byte, parser *PDFParser) ParseResult {
+	if len(data) == 0 {
+		return emptyPDFResult(filename)
+	}
+	baseURL := strings.TrimSpace(parser.PaddleOCRBaseURL)
+	if baseURL == "" {
+		baseURL = strings.TrimSpace(os.Getenv("PADDLEOCR_BASE_URL"))
+	}
+	if baseURL == "" {
+		baseURL = strings.TrimSpace(os.Getenv("PADDLEOCR_API_URL"))
+	}
+	if baseURL == "" {
+		return ParseResult{Err: fmt.Errorf("parser: PaddleOCR requires paddleocr_base_url or PADDLEOCR_BASE_URL")}
+	}
+	apiKey := parser.PaddleOCRAPIKey
+	if strings.TrimSpace(apiKey) == "" {
+		apiKey = strings.TrimSpace(os.Getenv("PADDLEOCR_ACCESS_TOKEN"))
+	}
+	algorithm := strings.TrimSpace(parser.PaddleOCRAlgorithm)
+	if algorithm == "" {
+		algorithm = strings.TrimSpace(os.Getenv("PADDLEOCR_ALGORITHM"))
+	}
+	if algorithm == "" {
+		algorithm = "PaddleOCR-VL"
+	}
+
+	driver := models.NewPaddleOCRLocalModel(
+		map[string]string{"default": baseURL},
+		models.URLSuffix{OCR: "layout-parsing"},
+	)
+	apiConfig := &models.APIConfig{
+		BaseURL: &baseURL,
+	}
+	if apiKey != "" {
+		apiConfig.ApiKey = &apiKey
+	}
+
+	resp, err := driver.OCRFile(&algorithm, data, &filename, apiConfig, &models.OCRConfig{
+		Algorithm: algorithm,
+	})
+	if err != nil {
+		return ParseResult{Err: fmt.Errorf("parser: PaddleOCR OCRFile: %w", err)}
+	}
+	if resp == nil || resp.Text == nil {
+		return ParseResult{Err: fmt.Errorf("parser: PaddleOCR returned empty text")}
+	}
+	pageCount := 1
+	if resp.Text != nil && strings.TrimSpace(*resp.Text) == "" {
+		pageCount = 0
+	}
+	return parseMinerUMarkdownResult(filename, *resp.Text, parser.OutputFormat, pageCount)
+}