fix(pipeline): query shortcuts + schema preview + serving meta fallback

- Add Shift+Enter shortcut to execute query (alongside Cmd/Ctrl+Enter)
- Add ▶ preview button to schema sidebar tables: populates editor with
  SELECT * FROM serving.<table> LIMIT 100 and auto-submits
- Update hint text to show "Shift+Enter to run"
- Overview tab: fall back to information_schema when _serving_meta.json
  is absent instead of showing error message; row counts show "—"
- Dashboard stat cards: same fallback — query DuckDB for table count

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

web/src/padelnomics/admin/pipeline_routes.py

@@ -372,11 +372,22 @@ def _is_stale(run: dict) -> bool:
 @role_required("admin")
 async def pipeline_dashboard():
     """Main page: health stat cards + tab container."""
-    summary = await asyncio.to_thread(_fetch_extraction_summary_sync)
-    serving_meta = await asyncio.to_thread(_load_serving_meta)
+    from .analytics import fetch_analytics  # noqa: PLC0415
 
-    total_serving_tables = len(serving_meta["tables"]) if serving_meta else 0
-    last_export = serving_meta.get("exported_at_utc", "")[:19].replace("T", " ") if serving_meta else "—"
+    summary, serving_meta = await asyncio.gather(
+        asyncio.to_thread(_fetch_extraction_summary_sync),
+        asyncio.to_thread(_load_serving_meta),
+    )
+
+    if serving_meta:
+        total_serving_tables = len(serving_meta.get("tables", {}))
+        last_export = serving_meta.get("exported_at_utc", "")[:19].replace("T", " ") or "—"
+    else:
+        schema_rows = await fetch_analytics(
+            "SELECT COUNT(*) AS n FROM information_schema.tables WHERE table_schema = 'serving'"
+        )
+        total_serving_tables = schema_rows[0]["n"] if schema_rows else 0
+        last_export = "—"
 
     success_rate = 0
     if summary["total"] > 0:
@@ -422,12 +433,30 @@ async def pipeline_overview():
     # Compute landing zone totals
     total_landing_bytes = sum(s["total_bytes"] for s in landing_stats)
 
+    # Build serving tables list: prefer _serving_meta.json (has counts + timestamp),
+    # fall back to information_schema when file doesn't exist yet.
+    if serving_meta:
+        serving_tables = [
+            {"name": name, "row_count": meta.get("row_count")}
+            for name, meta in sorted(serving_meta.get("tables", {}).items())
+        ]
+        last_export = serving_meta.get("exported_at_utc", "")[:19].replace("T", " ") or None
+    else:
+        from .analytics import fetch_analytics  # noqa: PLC0415
+        schema_rows = await fetch_analytics(
+            "SELECT table_name FROM information_schema.tables "
+            "WHERE table_schema = 'serving' ORDER BY table_name"
+        )
+        serving_tables = [{"name": r["table_name"], "row_count": None} for r in schema_rows]
+        last_export = None
+
     return await render_template(
         "admin/partials/pipeline_overview.html",
         workflow_rows=workflow_rows,
         landing_stats=landing_stats,
         total_landing_bytes=total_landing_bytes,
-        serving_meta=serving_meta,
+        serving_tables=serving_tables,
+        last_export=last_export,
         format_bytes=_format_bytes,
     )