Add song aliases to TOC and fix page numbering

- 82 songs get alias entries (alternate titles/opening lines) shown
  in italic in the TOC, pointing to the same page as the main title
- Front matter (title, foreword, TOC) has no page numbers
- Song pages start at page 1
- Aliases extracted from reference PDF (CL6) TOC by title matching

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

songs/karl-der-kaefer.tex

@@ -1,5 +1,6 @@
 \begin{song}{
   title = {Karl der Käfer},
+  alias = {Tief im Wald},
   lyrics = {Gänsehaut},
   composer = {Gänsehaut},
   bulibu = 306,