fix(content): handle None values in template pattern rendering

DuckDB rows can have NULL columns (e.g. market_score, median_peak_rate).
Replace None with 0 in render context so numeric Jinja2 filters like
round() and int don't crash with "NoneType doesn't define __round__".

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

web/src/padelnomics/content/__init__.py

@@ -12,7 +12,7 @@ from pathlib import Path
 
 import mistune
 import yaml
-from jinja2 import Environment
+from jinja2 import ChainableUndefined, Environment
 
 from ..analytics import fetch_analytics
 from ..core import execute, fetch_one, slugify
@@ -146,10 +146,12 @@ def _datetimeformat(value: str, fmt: str = "%Y-%m-%d") -> str:
 
 def _render_pattern(pattern: str, context: dict) -> str:
     """Render a Jinja2 pattern string with context variables."""
-    env = Environment()
+    env = Environment(undefined=ChainableUndefined)
     env.filters["slugify"] = slugify
     env.filters["datetimeformat"] = _datetimeformat
-    return env.from_string(pattern).render(**context)
+    # Replace None values with 0 so numeric filters (round, int) don't crash
+    safe_context = {k: (v if v is not None else 0) for k, v in context.items()}
+    return env.from_string(pattern).render(**safe_context)
 
 
 def _extract_faq_pairs(markdown: str) -> list[dict]: