feat(wordpress): set post category from title and tag rules

Published articles carried no category, so WordPress filed all of them
under the catch-all "Allgemein" - 941 of 955 posts by the time this was
noticed. The rules here mirror the one-off backfill of 2026-07-31 and
reproduce its result on all 955 posts exactly.

Matching is done on word boundaries rather than plain substrings, which
otherwise filed a campsite in Klagenfurt under "Recht & Vorschriften" via
the keyword "klage". German compounds opt in explicitly with a trailing
"*". A clear discount signal takes precedence over the product topic,
because product tags otherwise outnumber it.

Unknown slugs are never auto-created: unlike tags, the category set is
curated in WordPress, so a mismatch should surface rather than spawn a
new category. Articles that match no rule stay uncategorised on purpose.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/tests/test_categorize.py

@@ -0,0 +1,61 @@
+import unittest
+
+from backend.app.categorize import CATEGORY_SLUGS, category_slug, classify
+
+
+class TestCategorize(unittest.TestCase):
+    def test_tags_decide_the_category(self) -> None:
+        self.assertEqual(
+            classify("Neuer Platz am Wasser", ["Campingplatz", "5-Sterne-Campingplätze"]),
+            "campingplaetze",
+        )
+        self.assertEqual(classify("Unterwegs im Norden", ["Nordsee", "Niedersachsen"]), "reiseziele")
+        self.assertEqual(classify("Update vom Van", ["Wohnmobil", "Truma", "Solar"]), "fahrzeug-technik")
+
+    def test_title_alone_is_enough(self) -> None:
+        self.assertEqual(classify("Dometic CFX5 45 im Test: Top-Kühlbox", []), "ausruestung-tests")
+        self.assertEqual(classify("Führerscheine müssen getauscht werden", []), "recht-vorschriften")
+
+    def test_discount_signal_beats_the_product_topic(self) -> None:
+        # Without the override this lands in "Ausruestung & Tests", because the
+        # product tags outnumber the single discount signal.
+        self.assertEqual(
+            classify("Campingzelte bei Amazon im Sale: bis zu 55 %", ["Zelte", "Schlafsack", "Rabatt"]),
+            "angebote-rabatte",
+        )
+
+    def test_keywords_respect_word_boundaries(self) -> None:
+        # "klage" must not match the city name "Klagenfurt" - plain substring
+        # matching filed this campsite opening under "Recht & Vorschriften".
+        self.assertEqual(
+            classify("Falkensteiner Camping Wörthersee startet in die erste Saison",
+                     ["Campingplatz", "Klagenfurt", "Saisonstart"]),
+            "campingplaetze",
+        )
+
+    def test_compound_nouns_only_match_with_opt_in(self) -> None:
+        # "campingplatz*" is marked as a compound, so this still matches.
+        self.assertEqual(classify("Was Campingplatzbetreiber jetzt planen", []), "campingplaetze")
+
+    def test_returns_none_when_nothing_matches(self) -> None:
+        self.assertIsNone(classify("Weihnachten 2021", ["Weihnachten"]))
+        self.assertIsNone(category_slug("Weihnachten 2021", ["Weihnachten"]))
+
+    def test_umlauts_and_entities_are_normalised(self) -> None:
+        self.assertEqual(classify("Stellplätze an der Küste", []), "stellplaetze")
+        self.assertEqual(classify("Ausrüstung", ["Schlafsack"]), "ausruestung-tests")
+
+    def test_renamed_categories_keep_their_original_slug(self) -> None:
+        # Both were renamed in WordPress but kept the indexed archive URL.
+        self.assertEqual(CATEGORY_SLUGS["fahrzeug-technik"], "fahrzeug")
+        self.assertEqual(CATEGORY_SLUGS["news-branche"], "news")
+        self.assertEqual(category_slug("Update vom Van", ["Wohnmobil", "Truma"]), "fahrzeug")
+
+    def test_every_rule_maps_to_a_known_slug(self) -> None:
+        self.assertEqual(len(CATEGORY_SLUGS), 11)
+        for key, slug in CATEGORY_SLUGS.items():
+            self.assertTrue(slug and slug.islower(), f"{key} has a suspicious slug: {slug!r}")
+
+
+if __name__ == "__main__":
+    unittest.main()