fix: handle oversized lines in DB dump validation

Replace bufio.Scanner with bufio.Reader.ReadLine() which gracefully
skips lines exceeding the buffer (isPrefix=true) instead of failing.
Fixes validation of Immich's PostgreSQL dump which contains COPY lines
with binary-encoded image data exceeding the 256KB scanner limit.

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

controller/internal/backup/dbdump.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"context"
 	"fmt"
+	"io"
 	"log"
 	"os"
 	"os/exec"
@@ -259,15 +260,34 @@ func ValidateDump(filePath string, dbType DBType) DumpValidation {
 	}
 	defer f.Close()
 
-	scanner := bufio.NewScanner(f)
-	// Increase token buffer for very long lines (some SQL lines can be large)
-	scanner.Buffer(make([]byte, 256*1024), 256*1024)
+	// Use bufio.Reader instead of Scanner: ReadLine gracefully handles lines
+	// longer than the buffer (isPrefix=true) so we can skip them. Only short
+	// lines matter (headers, CREATE TABLE). Long COPY/INSERT data lines
+	// (e.g., Immich's binary-encoded image data) are skipped without allocating.
+	reader := bufio.NewReaderSize(f, 256*1024)
 
 	lineNum := 0
 	headerFound := false
 	tableCount := 0
-	for scanner.Scan() {
-		line := scanner.Text()
+	for {
+		lineBytes, isPrefix, err := reader.ReadLine()
+		if err != nil {
+			if err != io.EOF {
+				v.Error = fmt.Sprintf("hiba az olvasás közben: %v", err)
+				log.Printf("[WARN] ValidateDump FAIL: %s — read error: %v", filePath, err)
+				return v
+			}
+			break // EOF
+		}
+		if isPrefix {
+			// Line exceeds buffer — skip remainder (COPY data, large INSERTs)
+			for isPrefix && err == nil {
+				_, isPrefix, err = reader.ReadLine()
+			}
+			continue
+		}
+
+		line := string(lineBytes)
 		lineNum++
 
 		// Header check — scan first 10 lines for expected dump header
@@ -294,12 +314,6 @@ func ValidateDump(filePath string, dbType DBType) DumpValidation {
 		}
 	}
 
-	if err := scanner.Err(); err != nil {
-		v.Error = fmt.Sprintf("hiba az olvasás közben: %v", err)
-		log.Printf("[WARN] ValidateDump FAIL: %s — scanner error: %v", filePath, err)
-		return v
-	}
-
 	v.TableCount = tableCount
 
 	if !headerFound {