fix: move scanner.Err() check after loop and fix matches bounds check

Two bugs in ExtractMeta:

1. scanner.Err() was checked inside the Scan() loop. According to the
   bufio.Scanner docs, Err() returns nil during a successful scan; it
   only reflects an error after Scan() returns false. Moving the check
   after the loop ensures real I/O errors are surfaced instead of
   silently ignored.

2. The len(matches) guard was 'len(matches) > 1' but the code
   accessed matches[2] (requires len >= 3). reHeaderPatternV2 always
   produces a 3-element slice when it matches, but the condition was
   misleading and could panic if the regex were ever changed to make
   the second capture group optional. Changed to 'len(matches) > 2'.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

metadata/metadata.go

@@ -63,10 +63,6 @@ func ExtractMeta(data []byte, spaceFromCli string, titleFromH1 bool, titleFromFi
 	for scanner.Scan() {
 		line := scanner.Text()
 
-		if err := scanner.Err(); err != nil {
-			return nil, nil, err
-		}
-
 		offset += len(line) + 1
 
 		matches := reHeaderPatternV2.FindStringSubmatch(line)
@@ -88,7 +84,7 @@ func ExtractMeta(data []byte, spaceFromCli string, titleFromH1 bool, titleFromFi
 		header := cases.Title(language.English).String(matches[1])
 
 		var value string
-		if len(matches) > 1 {
+		if len(matches) > 2 {
 			value = strings.TrimSpace(matches[2])
 		}
 
@@ -147,6 +143,10 @@ func ExtractMeta(data []byte, spaceFromCli string, titleFromH1 bool, titleFromFi
 		}
 	}
 
+	if err := scanner.Err(); err != nil {
+		return nil, nil, err
+	}
+
 	if titleFromH1 || titleFromFilename || spaceFromCli != "" {
 		if meta == nil {
 			meta = &Meta{}