feat: OCR scans with tesseract, drop docling from the default path. (#33)

pdftotext still wins on born-digital PDFs. Empty text layers go through
pdftoppm + tesseract eng+deu. Optional OCR_ENGINE=paddle. Gitea #6.

bin/mail/ocr.go

@@ -0,0 +1,48 @@
+//usr/bin/env go run -tags=mail_ocr "$0" "$@"; exit
+//go:build mail_ocr
+//
+// bin/mail/ocr.go - OCR an image or scanned PDF (tesseract eng+deu).
+//
+//	./bin/mail/ocr.go scan.png
+//	./bin/mail/ocr.go scan.pdf
+//	OCR_ENGINE=paddle ./bin/mail/ocr.go scan.png
+//
+// PDFs try pdftotext -layout first; empty text layer uses pdftoppm + tesseract.
+// No gocv. Tesseract CGO bindings are not used (D21 Zig owns Ladybug CGO).
+// NOTE: never run `gofmt -w` on this file — it breaks the shebang.
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/eSlider/2dph/internal/ocr"
+)
+
+func main() {
+	os.Exit(run(os.Args[1:]))
+}
+
+func run(args []string) int {
+	if len(args) != 1 || strings.HasPrefix(args[0], "-") {
+		fmt.Fprintln(os.Stderr, `usage: bin/mail/ocr.go <image|pdf>`)
+		return 2
+	}
+	path := args[0]
+	var (
+		text string
+		err  error
+	)
+	if strings.HasSuffix(strings.ToLower(path), ".pdf") {
+		text, err = ocr.PDFFile(path)
+	} else {
+		text, err = ocr.ImageFile(path)
+	}
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "mail/ocr: %v\n", err)
+		return 1
+	}
+	fmt.Println(text)
+	return 0
+}