fix(content): add missing datetimeformat filter; move preview column first

- Add _datetimeformat Jinja2 filter to _render_pattern() — templates
  use {{ 'now' | datetimeformat('%Y') }} but the filter was never
  registered, causing "No filter named 'datetimeformat'" on preview.
- Move Preview button to first column in template detail data table
  so it's visible without scrolling on wide tables.

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

web/src/padelnomics/admin/templates/admin/template_detail.html

@@ -81,24 +81,24 @@
       <table class="table text-sm">
         <thead>
           <tr>
+            <th></th>
             {% for col in columns %}
             <th>{{ col.name }}</th>
             {% endfor %}
-            <th>Preview</th>
           </tr>
         </thead>
         <tbody>
           {% for row in sample_rows %}
           <tr>
+            <td>
+              <a href="{{ url_for('admin.template_preview', slug=config_data.slug, row_key=row[config_data.natural_key]) }}"
+                 class="btn-outline btn-sm">Preview</a>
+            </td>
             {% for col in columns %}
             <td class="mono" style="max-width:200px; overflow:hidden; text-overflow:ellipsis; white-space:nowrap">
               {{ row[col.name] }}
             </td>
             {% endfor %}
-            <td>
-              <a href="{{ url_for('admin.template_preview', slug=config_data.slug, row_key=row[config_data.natural_key]) }}"
-                 class="btn-outline btn-sm">Preview</a>
-            </td>
           </tr>
           {% endfor %}
         </tbody>

web/src/padelnomics/content/__init__.py

@@ -133,10 +133,22 @@ def _validate_table_name(data_table: str) -> None:
 
 # ── Rendering helpers ────────────────────────────────────────────────────────
 
+def _datetimeformat(value: str, fmt: str = "%Y-%m-%d") -> str:
+    """Jinja2 filter: format a date string (or 'now') with strftime."""
+    from datetime import datetime, UTC
+
+    if value == "now":
+        dt = datetime.now(UTC)
+    else:
+        dt = datetime.fromisoformat(value)
+    return dt.strftime(fmt)
+
+
 def _render_pattern(pattern: str, context: dict) -> str:
     """Render a Jinja2 pattern string with context variables."""
     env = Environment()
     env.filters["slugify"] = slugify
+    env.filters["datetimeformat"] = _datetimeformat
     return env.from_string(pattern).render(**context)