fix(content): slugify transliteration + article links + country overview ranking

- Add @slugify SQLMesh macro (STRIP_ACCENTS + ß→ss) replacing broken
  inline REGEXP_REPLACE that dropped non-ASCII chars (Düsseldorf → d-sseldorf)
- Apply @slugify to dim_venues, dim_cities, dim_locations
- Fix Python slugify() to pre-replace ß→ss before NFKD normalization
- Add language prefix to B2B article market links (/markets/germany → /de/markets/germany)
- Change country overview top-5 ranking: venue count (not raw market_score)
  for top cities, population for top opportunity cities

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/padelnomics/core.py

@@ -740,9 +740,14 @@ async def get_all_paddle_prices() -> dict[str, str]:
 
 
 def slugify(text: str, max_length_chars: int = 80) -> str:
-    """Convert text to URL-safe slug."""
+    """Convert text to URL-safe slug.
+
+    Pre-replaces ß→ss before NFKD normalization so output matches the SQL
+    @slugify macro (which uses DuckDB STRIP_ACCENTS + REPLACE).
+    """
+    text = text.lower().replace("ß", "ss")
     text = unicodedata.normalize("NFKD", text).encode("ascii", "ignore").decode()
-    text = re.sub(r"[^\w\s-]", "", text.lower())
+    text = re.sub(r"[^\w\s-]", "", text)
     text = re.sub(r"[-\s]+", "-", text).strip("-")
     return text[:max_length_chars]