feat: Phase 1 – Konten, Kategorien, Transaktionen, EZB-Währungsumrechnung

Backend:
- Modelle + Migration 0002: accounts, account_identifiers, category_groups,
  categories, transactions, exchange_rates (alle owner-gescoped).
- EZB-Kursdienst (90-Tage/Historie) + Backfill-Skript; Umrechnung EUR<->CHF zum
  Buchungsdatum mit lokalem Cache und manueller Übersteuerung; EUR-Pivot
  (amount_eur_cents) eingefroren.
- Kontostände + Netto-Vermögen (Umrechnung in Hauptwährung).
- Router: accounts (inkl. IBAN-Identifikatoren), categories (Gruppen+Kategorien),
  transactions (Ausgabe/Einnahme/Transfer, cross-currency), rates.
- Gruppierte Standard-Kategorien je Nutzer beim Anlegen.
- pytest-Suite: Währung, Salden, Cross-Currency-Transfer, Nutzer-Isolation.

Frontend:
- Seiten Konten, Kategorien, Buchungen; Icon-Chip, Geldbetrag mit Umrechnung,
  Icon-/Farbwähler, Modal; erweitertes SVG-Icon-Set (Konto-/Kategorie-Icons).
- Währungs-/Datumsformatierung (EUR de-DE, CHF de-CH), i18n DE/EN erweitert.
- Live-Umrechnungs-Vorschau im Transfer-Formular.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/routers/accounts.py

@@ -0,0 +1,137 @@
+"""Konten inkl. Erkennungs-Identifikatoren. Alles owner-gescoped."""
+
+from datetime import date
+
+from fastapi import APIRouter, Depends, status
+from sqlalchemy.orm import Session
+
+from ..database import get_db
+from ..deps import get_current_user, get_owned
+from ..models import Account, AccountIdentifier, User
+from ..schemas import AccountCreate, AccountIdentifierOut, AccountOut, AccountUpdate
+from ..services import balances
+from .settings import BASE_CURRENCY_KEY, get_user_setting
+
+router = APIRouter(prefix="/accounts", tags=["accounts"])
+
+
+def normalize_identifier(value: str) -> str:
+    """Vereinheitlicht IBAN/Nummer für den Abgleich: Großbuchstaben, nur alphanumerisch."""
+    return "".join(ch for ch in value.upper() if ch.isalnum())
+
+
+def base_currency(db: Session, user: User) -> str:
+    return get_user_setting(db, user, BASE_CURRENCY_KEY) or "EUR"
+
+
+def to_out(db: Session, acc: Account, base: str, on: date) -> AccountOut:
+    return AccountOut(
+        id=acc.id,
+        name=acc.name,
+        type=acc.type,
+        currency=acc.currency,
+        icon=acc.icon,
+        color=acc.color,
+        opening_balance_cents=acc.opening_balance_cents,
+        opening_date=acc.opening_date,
+        is_archived=acc.is_archived,
+        position=acc.position,
+        identifiers=[
+            AccountIdentifierOut(id=i.id, kind=i.kind, value=i.value) for i in acc.identifiers
+        ],
+        balance_cents=balances.account_balance_cents(db, acc),
+        balance_base_cents=balances.account_balance_base_cents(db, acc, base, on),
+    )
+
+
+def _set_identifiers(acc: Account, items) -> None:
+    """Ersetzt die Identifikator-Liste (dedupliziert nach Art + Normalform)."""
+    acc.identifiers.clear()
+    seen: set[tuple[str, str]] = set()
+    for it in items:
+        norm = normalize_identifier(it.value)
+        key = (it.kind.value, norm)
+        if not norm or key in seen:
+            continue
+        seen.add(key)
+        acc.identifiers.append(
+            AccountIdentifier(kind=it.kind, value=it.value.strip(), value_norm=norm)
+        )
+
+
+@router.get("", response_model=list[AccountOut])
+def list_accounts(db: Session = Depends(get_db), user: User = Depends(get_current_user)):
+    base = base_currency(db, user)
+    today = date.today()
+    accounts = (
+        db.query(Account)
+        .filter(Account.owner_id == user.id)
+        .order_by(Account.position, Account.name)
+        .all()
+    )
+    return [to_out(db, a, base, today) for a in accounts]
+
+
+@router.post("", response_model=AccountOut, status_code=status.HTTP_201_CREATED)
+def create_account(
+    payload: AccountCreate, db: Session = Depends(get_db), user: User = Depends(get_current_user)
+):
+    max_pos = (
+        db.query(Account.position)
+        .filter(Account.owner_id == user.id)
+        .order_by(Account.position.desc())
+        .first()
+    )
+    acc = Account(
+        owner_id=user.id,
+        name=payload.name.strip(),
+        type=payload.type,
+        currency=payload.currency,
+        icon=payload.icon,
+        color=payload.color,
+        opening_balance_cents=payload.opening_balance_cents,
+        opening_date=payload.opening_date,
+        position=(max_pos[0] + 1) if max_pos else 0,
+    )
+    _set_identifiers(acc, payload.identifiers)
+    db.add(acc)
+    db.commit()
+    db.refresh(acc)
+    return to_out(db, acc, base_currency(db, user), date.today())
+
+
+@router.get("/{account_id}", response_model=AccountOut)
+def get_account(
+    account_id: int, db: Session = Depends(get_db), user: User = Depends(get_current_user)
+):
+    acc = get_owned(db, Account, account_id, user)
+    return to_out(db, acc, base_currency(db, user), date.today())
+
+
+@router.patch("/{account_id}", response_model=AccountOut)
+def update_account(
+    account_id: int,
+    payload: AccountUpdate,
+    db: Session = Depends(get_db),
+    user: User = Depends(get_current_user),
+):
+    acc = get_owned(db, Account, account_id, user)
+    data = payload.model_dump(exclude_unset=True)
+    identifiers = data.pop("identifiers", None)
+    for key, value in data.items():
+        if value is not None or key in ("opening_date",):
+            setattr(acc, key, value)
+    if identifiers is not None:
+        _set_identifiers(acc, payload.identifiers)
+    db.commit()
+    db.refresh(acc)
+    return to_out(db, acc, base_currency(db, user), date.today())
+
+
+@router.delete("/{account_id}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_account(
+    account_id: int, db: Session = Depends(get_db), user: User = Depends(get_current_user)
+):
+    acc = get_owned(db, Account, account_id, user)
+    db.delete(acc)
+    db.commit()