fix: add missing tier fields to signup page context

Add orders_per_month, team_members, and is_enterprise to tier data
passed to the signup template.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/routes/platform_pages.py

@@ -239,6 +239,9 @@ async def signup_page(
             "name": limits["name"],
             "price_monthly": limits["price_monthly_cents"] / 100,
             "price_annual": (limits["price_annual_cents"] / 100) if limits.get("price_annual_cents") else None,
+            "orders_per_month": limits.get("orders_per_month"),
+            "team_members": limits.get("team_members"),
+            "is_enterprise": tier_code == TierCode.ENTERPRISE,
         })
 
     context["tiers"] = tiers