feat(enrich): full category taxonomy, tighter description + opening_hours rules (B1-B3)

- Replace 3-example inline comment with 7-label taxonomy block so the
  model knows all valid categories instead of guessing from partial hints
- Tighten description constraint to 60-220 chars with explicit word bans
- Mark opening_hours as a rough guide, not authoritative for booking

backend/internal/domain/discovery/enrich/llm_enricher.go

@@ -141,15 +141,34 @@ DACH region. Using the provided source-page excerpts as grounding, return a
 JSON object with exactly these fields:
 
   {
-    "category": string,         // short German label, e.g. "mittelaltermarkt",
-                                // "weihnachtsmarkt", "ritterfest". Lowercase.
-    "opening_hours": string,    // German; brief (e.g. "Sa-So 10:00-18:00").
+    "category": string,   // see taxonomy below
+    "opening_hours": string,    // Brief German summary, e.g. "Sa-So 10:00-18:00".
+                                // Rough guide only — not authoritative for booking.
                                 // Empty string if unclear from sources.
-    "description": string       // 1-3 sentences in German summarising what the
-                                // market offers. Neutral tone, no hype.
-                                // Empty string if sources have no useful info.
+    "description": string   // 60-220 chars, German, complete sentences, neutral
+                            // tone. No lists, no marketing words (einzigartig,
+                            // unvergesslich, magisch). Facts only. Empty string
+                            // if sources have no useful content.
+                            // Example: "Dreitaegiger Mittelaltermarkt mit
+                            // Haendlern, Lagerleben und Ritterturnieren."
   }
 
+Category taxonomy — pick exactly one:
+  mittelaltermarkt   Medieval market: merchants, craft stalls, period costumes
+  weihnachtsmarkt    Christmas market / Advent market
+  ritterfest         Knight festival: jousting, tournaments, knight camp focus
+  handwerkermarkt    Craft/artisan market without strong medieval theme
+  schlossfest        Castle or palace festival — broader programme, not just market
+  ritterturnier      Jousting tournament; the tournament IS the main event
+  kirchweih          Traditional Bavarian/Austrian parish fair (Kirmes, Kirtag)
+  (empty string)     Sources unclear or event does not fit any category above
+
+Examples:
+  "Dresdner Striezelmarkt", christmas-market sources  →  "weihnachtsmarkt"
+  "Ritterturnier Burg Kreuzenstein", jousting sources  →  "ritterturnier"
+  "Kirchweih Fürth", parish-fair sources               →  "kirchweih"
+  "Schlossfest Schönbrunn", castle-festival sources    →  "schlossfest"
+
 Rules:
 - Return ONLY the JSON object. No prose, no code fences.
 - If the sources do not support a field, return an empty string for it.