Fix chapter reader nav bar: use hamburger icon for back-to-book, show chapter date below title

- Replace bare ← back-to-book link with ☰ (hamburger) icon to eliminate
  the visual double-arrow confusion with the ← Prev chapter button
- Export SplitChapterTitle in writer package and call it in handleChapter
  to split the raw heading into (title, date) — fixes concatenated title+date bug
- Display ChapterDate as a smaller muted line below the chapter title
  in the center nav button
- Bump nav bar height from h-12 to h-14 to accommodate two-line center button

scraper/internal/writer/writer.go

@@ -219,12 +219,12 @@ func chapterTitle(path string, n int) (title, date string) {
 			continue
 		}
 		line = strings.TrimPrefix(line, "# ")
-		return splitChapterTitle(line)
+		return SplitChapterTitle(line)
 	}
 	return fmt.Sprintf("Chapter %d", n), ""
 }
 
-// splitChapterTitle separates the human-readable chapter name from the
+// SplitChapterTitle separates the human-readable chapter name from the
 // trailing relative-date string that novelfire.net appends to the heading.
 // Examples of raw heading text (after stripping "# "):
 //
@@ -233,7 +233,7 @@ func chapterTitle(path string, n int) (title, date string) {
 //
 // The pattern is: optional leading number+whitespace, then the real title,
 // then a date that matches /\d+\s+(second|minute|hour|day|week|month|year)s?\s+ago$/
-func splitChapterTitle(raw string) (title, date string) {
+func SplitChapterTitle(raw string) (title, date string) {
 	// Strip a leading chapter-number index that novelfire sometimes prepends.
 	// It looks like "1   " or "12  " at the very start.
 	raw = strings.TrimSpace(raw)