fix: recognise forum rows in the list view

A viewforum page is not always a list of topics — a category page lists
forums, and a forum page can carry both. Every row was treated as a topic,
so on those pages the only link the row offered was the icon in its last-post
column: the forum name was dropped, its description ended up in the muted
footer line, and nothing was left to tap. Moving between forums on a phone
was impossible.

Rows are now classified by their first usable link, which relies on document
order: a forum row names the forum before it links the last post. Detection
prefers phpBB's own classes and falls back to the shape of the row, because
the board runs a custom theme whose markup could not be verified — the page
requires a login.

That fallback needs a brake. The page scaffolding is itself a table, so a
link outside any list row resolves to a row containing the whole document,
which passed for a forum row and turned the page header, a stylesheet and
inline scripts into a forum description. Rows carrying nested tables, forms
or scripts are therefore rejected, and descriptions are read only from the
title cell's own text.

README.md

@@ -15,10 +15,18 @@ page type:
 
 | Page | View |
 |---|---|
-| `viewforum.php`, `search.php`, forum root | Topic list as cards |
+| `viewforum.php`, `search.php`, forum root | Topic and forum list as cards |
 | `viewtopic.php` | Thread as a post stream with a fixed bottom navigation bar |
 | anything else | Untouched — no styles are injected |
 
+A `viewforum.php` page is not necessarily a list of topics: a category page
+lists forums instead, and a forum page can carry both. Each table row is
+therefore classified by its first usable link. Forum rows become cards with
+name, description, subforum links and counts; topic rows keep their existing
+card; category headers become section headings. Rows are recognised by phpBB's
+own `forumlink` / `forumdesc` classes, and failing that by their shape — two
+purely numeric columns are only ever a forum's topic and post count.
+
 The thread navigation bar holds first / previous / next / last and a page
 indicator. Tapping the indicator opens a sheet with a number field and a grid of
 all pages. Targets are computed as `start = (page - 1) × per_page` rather than
@@ -178,10 +186,19 @@ anhand des Seitentyps:
 
 | Seite | Ansicht |
 |---|---|
-| `viewforum.php`, `search.php`, Forumwurzel | Themenliste als Karten |
+| `viewforum.php`, `search.php`, Forumwurzel | Themen- und Forenliste als Karten |
 | `viewtopic.php` | Thread als Beitragsstrom mit fixierter Navigationsleiste |
 | alles andere | Unverändert — es werden keine Stile injiziert |
 
+Eine `viewforum.php`-Seite ist nicht zwangsläufig eine Themenliste: eine
+Kategorieseite listet Foren auf, eine Forenseite kann beides enthalten. Jede
+Tabellenzeile wird deshalb anhand ihres ersten verwertbaren Links eingeordnet.
+Forenzeilen werden zu Karten mit Name, Beschreibung, Unterforen und Zahlen,
+Themenzeilen behalten ihre bisherige Karte, Kategoriezeilen werden zu
+Zwischenüberschriften. Erkannt werden die Zeilen an phpBBs eigenen Klassen
+`forumlink` / `forumdesc` und ersatzweise an ihrer Form — zwei rein numerische
+Spalten hat nur eine Forenzeile mit Themen- und Beitragszahl.
+
 Die Navigationsleiste im Thread enthält erste / vorherige / nächste / letzte
 Seite und eine Positionsanzeige. Ein Tipp darauf öffnet ein Sheet mit
 Zahlenfeld und einem Raster aller Seiten. Die Ziele werden als