Phase 6: Translate User Pages - exchange, trades, invites, profile

- Expand exchange.json with all exchange page strings (page, steps, detailsStep, bookingStep, confirmationStep, priceDisplay)
- Create trades.json translation files for es, en, ca
- Create invites.json translation files for es, en, ca
- Create profile.json translation files for es, en, ca
- Translate exchange page and all components (ExchangeDetailsStep, BookingStep, ConfirmationStep, StepIndicator, PriceDisplay)
- Translate trades page (titles, sections, buttons, status labels)
- Translate invites page (titles, sections, status badges, copy button)
- Translate profile page (form labels, hints, placeholders, messages)
- Update IntlProvider to load all new namespaces
- All frontend tests passing

frontend/locales/ca/trades.json

@@ -0,0 +1,16 @@
+{
+  "page": {
+    "title": "Les Meves Operacions",
+    "subtitle": "Veure i gestionar les teves operacions de Bitcoin",
+    "loadingTrades": "Carregant operacions...",
+    "noTrades": "Encara no tens operacions.",
+    "startTrading": "Començar a operar",
+    "upcoming": "Properes ({count})",
+    "history": "Historial ({count})"
+  },
+  "trade": {
+    "rate": "Taxa:",
+    "cancel": "Cancel·lar",
+    "viewDetails": "Veure Detalls"
+  }
+}