Add user settings endpoint and exchange rate fallback APIs

Backend now stores user settings (dashboard config) in a JSONB column and
exposes CRUD via /settings/. Exchange rate service gains multiple fallback
providers (ExchangeRate-API, currency-api, FloatRates) so USD/CRC rates
stay available when BCCR is down.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/api/v1/endpoints/settings.py

@@ -0,0 +1,59 @@
+from datetime import datetime
+
+from fastapi import APIRouter, Depends
+from sqlmodel import Session, select
+
+from app.auth import get_current_user
+from app.db import get_session
+from app.models.models import UserSettings, UserSettingsRead, UserSettingsUpdate
+
+router = APIRouter(prefix="/settings", tags=["settings"])
+
+DEFAULT_SETTINGS = {
+    "dashboard": {
+        "sections": {
+            "crc_accounts": {"label": "CRC Accounts", "color": "primary", "cardColor": "primary", "visible": True, "order": 0, "expanded": False},
+            "usd_accounts": {"label": "USD Accounts", "color": "chart-1", "cardColor": "chart-1", "visible": True, "order": 1, "expanded": False},
+            "pension": {"label": "Pension", "color": "chart-2", "cardColor": "chart-2", "visible": True, "order": 2, "expanded": False},
+            "savings": {"label": "Savings", "color": "chart-3", "cardColor": "chart-3", "visible": True, "order": 3, "expanded": False},
+            "liabilities": {"label": "Liabilities", "color": "destructive", "cardColor": "destructive", "visible": True, "order": 4, "expanded": False},
+            "crypto": {"label": "Crypto", "color": "chart-4", "cardColor": "chart-4", "visible": True, "order": 5, "expanded": False},
+        }
+    }
+}
+
+
+@router.get("/", response_model=UserSettingsRead)
+def get_settings(
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    settings = session.exec(
+        select(UserSettings).where(UserSettings.key == "default")
+    ).first()
+    if not settings:
+        settings = UserSettings(key="default", data=DEFAULT_SETTINGS)
+        session.add(settings)
+        session.commit()
+        session.refresh(settings)
+    return settings
+
+
+@router.patch("/", response_model=UserSettingsRead)
+def update_settings(
+    body: UserSettingsUpdate,
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    settings = session.exec(
+        select(UserSettings).where(UserSettings.key == "default")
+    ).first()
+    if not settings:
+        settings = UserSettings(key="default", data=body.data)
+    else:
+        settings.data = body.data
+    settings.updated_at = datetime.utcnow()
+    session.add(settings)
+    session.commit()
+    session.refresh(settings)
+    return settings