feat: write markdown to disk during generation for admin editing

- generate_articles() now writes body_md alongside body_html
  to BUILD_DIR/{lang}/md/{slug}.md
- article_edit GET checks both manual and generated markdown paths
- Fix pre-existing ruff import sort in _datetimeformat

Subtask 5 of CMS admin improvement.

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

web/src/padelnomics/admin/routes.py

@@ -1814,8 +1814,12 @@ async def article_edit(article_id: int):
         await flash("Article updated.", "success")
         return redirect(url_for("admin.articles"))
 
-    # Load markdown source if available
+    # Load markdown source if available (manual or generated)
+    from ..content.routes import BUILD_DIR as CONTENT_BUILD_DIR
     md_path = Path("data/content/articles") / f"{article['slug']}.md"
+    if not md_path.exists():
+        lang = article["language"] or "en"
+        md_path = CONTENT_BUILD_DIR / lang / "md" / f"{article['slug']}.md"
     body = md_path.read_text() if md_path.exists() else ""
 
     data = {**dict(article), "body": body}

web/src/padelnomics/content/__init__.py

@@ -135,7 +135,7 @@ def _validate_table_name(data_table: str) -> None:
 
 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
+    from datetime import UTC, datetime
 
     if value == "now":
         dt = datetime.now(UTC)
@@ -429,6 +429,11 @@ async def generate_articles(
             build_dir.mkdir(parents=True, exist_ok=True)
             (build_dir / f"{article_slug}.html").write_text(body_html)
 
+            # Write markdown source to disk (for admin editing)
+            md_dir = BUILD_DIR / lang / "md"
+            md_dir.mkdir(parents=True, exist_ok=True)
+            (md_dir / f"{article_slug}.md").write_text(body_md)
+
             # Upsert article in SQLite
             existing_article = await fetch_one(
                 "SELECT id FROM articles WHERE url_path = ?", (url_path,),