Phase 3.2: Add My Trades page

New /trades page for viewing user's Bitcoin trades:
- Upcoming trades with cancel functionality
- Trade history (completed, cancelled, no-show)
- Direction badges (BUY/SELL with colors)
- EUR ↔ BTC amounts in readable format
- Rate and premium display

Update Header navigation:
- Exchange replaces Book for regular users
- My Trades replaces Appointments

Update profile page test for new nav items.

frontend/app/components/Header.tsx

@@ -10,8 +10,8 @@ const { ADMIN, REGULAR } = constants.roles;
 type PageId =
   | "profile"
   | "invites"
-  | "booking"
-  | "appointments"
+  | "exchange"
+  | "trades"
   | "admin-invites"
   | "admin-availability"
   | "admin-appointments"
@@ -30,8 +30,8 @@ interface NavItem {
 }
 
 const REGULAR_NAV_ITEMS: NavItem[] = [
-  { id: "booking", label: "Book", href: "/booking", regularOnly: true },
-  { id: "appointments", label: "Appointments", href: "/appointments", regularOnly: true },
+  { id: "exchange", label: "Exchange", href: "/exchange", regularOnly: true },
+  { id: "trades", label: "My Trades", href: "/trades", regularOnly: true },
   { id: "invites", label: "My Invites", href: "/invites", regularOnly: true },
   { id: "profile", label: "My Profile", href: "/profile", regularOnly: true },
 ];