feat(dashboard): add country distribution bar chart using Chart.js

app/routers/web.py

@@ -397,6 +397,13 @@ def dashboard(request: Request, user: User = Depends(get_current_user_web), db:
     else:
         sent_pct = delivered_pct = received_pct = 0
 
+    # country stats
+    country_counts: dict[str, int] = {}
+    for c in all_cards:
+        if c.country:
+            country_counts[c.country] = country_counts.get(c.country, 0) + 1
+    country_stats = sorted(country_counts.items(), key=lambda x: -x[1])
+
     from datetime import datetime, timezone as _tz
 
     return templates.TemplateResponse("dashboard.html", {
@@ -404,6 +411,7 @@ def dashboard(request: Request, user: User = Depends(get_current_user_web), db:
         "total": total, "sent": sent, "delivered": delivered, "received": received,
         "countries": countries, "recent": recent,
         "sent_pct": sent_pct, "delivered_pct": delivered_pct, "received_pct": received_pct,
+        "country_stats": country_stats,
         "now": datetime.now(_tz.utc),
     })