fix: Pandoc-Weg – EPUB-Links, Formeln im EPUB, portables TeX (QA3-04 bis QA3-06)

Prüfung aller 5 Beispielbücher über die Befehle der Buch-README (HTML,
EPUB, PDF mit weasyprint und xelatex):

- QA3-04: Der EPUB-Befehl der Buch-README hatte kein --mathml; im
  Mathebuch blieben 1072 Formeln als TeX-Text. Jetzt 4904 als MathML.
- QA3-05: Kapitel-Startanker von epub2md_merge.py begannen mit einer
  Ziffer (039-…). Pandocs EPUB-Writer löst Links darauf nicht auf (C-Buch
  32, Mathebuch 20 tote Links). Jetzt kap-039-…; book.lua erkennt beide.
- QA3-06: portable_tex() passt Verlags-TeX für texmath an (\"u, \O,
  @{…} und \arraycolsep in array, leeres \displaystyle vor Zellenende).
  Mathebuch: 1 statt 9 nicht umsetzbare Formeln.
- Cover ohne Seitenzahl (print.css, book.lua).

Neue Tests: tests/test_pandoc.py (nur mit installiertem pandoc),
Parametertests für portable_tex. Andere Bücher byte-identisch.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pandoc/book.lua

@@ -11,7 +11,7 @@ This filter, for HTML output:
   * builds the table of contents at the placeholder (use it INSTEAD of --toc; --toc-depth is honoured),
   * drops Pandoc's title block when the book has its own title page, or moves it to the placeholder,
   * shows the cover (first chapter with nothing but one picture) without the caption "Cover",
-  * turns the chapter anchors <a id="001-…"></a> into <div class="chapter-start"> so that print.css can
+  * turns the chapter anchors <a id="kap-001-…"></a> into <div class="chapter-start"> so that print.css can
     start every chapter – including cover, title page and imprint – on a new page.
 
 For LaTeX (PDF route md -> html -> pdf, filter in BOTH steps, no --toc) the table of contents becomes
@@ -55,7 +55,7 @@ local function title_block(meta)
   return pandoc.RawBlock("html", table.concat(html, "\n"))
 end
 
--- Paragraph that only holds chapter start anchors (<a id="001-cover"></a>) → id of the first one.
+-- Paragraph that only holds chapter start anchors (<a id="kap-001-cover"></a>) → id of the first one.
 local function chapter_anchor(block)
   if block.t ~= "Para" and block.t ~= "Plain" then
     return nil
@@ -65,7 +65,8 @@ local function chapter_anchor(block)
     if inl.t ~= "RawInline" then
       return nil
     end
-    local found = inl.text:match('^<a id="(%d%d%d%-[^"]*)">$') or inl.text:match('^<a id="(%d%d%d%-[^"]*)"></a>$')
+    local found = inl.text:match('^<a id="(kap%-%d%d%d%-[^"]*)">$') or inl.text:match('^<a id="(kap%-%d%d%d%-[^"]*)"></a>$')
+      or inl.text:match('^<a id="(%d%d%d%-[^"]*)">$') or inl.text:match('^<a id="(%d%d%d%-[^"]*)"></a>$')  -- before 0.2.1
     if found then
       id = id or found
     elseif inl.text ~= "</a>" then
@@ -143,6 +144,7 @@ local function latex_book(doc)
       blocks:insert(pandoc.RawBlock("latex", "\\clearpage"))
       blocks:insert(block)
     elseif block.t == "Div" and block.classes:includes("cover") then
+      blocks:insert(pandoc.RawBlock("latex", "\\thispagestyle{empty}")) -- no page number on the cover
       blocks:insert(block:walk({ Image = function(img) -- cover as large as the page allows
         img.attributes.width = nil
         img.attributes.height = "20cm"