feat: Phase 4 – CSV-Import (Templates, Prüfansicht, Duplikat/Transfer-Erkennung, Undo)

Backend:
- Modelle + Migration 0005: import_templates, import_batches, categorization_rules;
  transactions um import_batch_id + import_hash erweitert.
- services/csv_import: Datei parsen (Trennzeichen, Dezimal-/Datumsformat, Kodierung,
  Header/Skip, Vorzeichen vs. Soll/Haben), Vorschau mit Duplikat-Erkennung (Hash),
  interner-Transfer-Erkennung via IBAN, lernender Auto-Kategorisierung; Buchen mit
  Batch und Undo.
- routers/imports: Templates (CRUD), Roh-Vorschau, Prüf-Vorschau, Buchen, Verlauf,
  Rückgängig. pytest: Parsing, Duplikate, Transfer, Buchen, Undo, Lernen.

Frontend:
- Import-Seite: Konto+Datei, Format/Spaltenzuordnung (mit Roh-Vorschau),
  editierbare Prüfansicht (Kategorie/Typ/Zielkonto, Duplikate markiert),
  Buchen, Import-Verlauf mit Undo; Vorlagen speichern; i18n DE/EN.

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

backend/app/models.py

@@ -84,6 +84,23 @@ class BudgetTreatment(str, enum.Enum):
     neutral = "neutral"
 
 
+class AmountMode(str, enum.Enum):
+    """Wie der Betrag in der CSV steht."""
+    signed = "signed"              # eine Spalte, mit Vorzeichen (− = Ausgabe)
+    debit_credit = "debit_credit"  # getrennte Soll-/Haben-Spalten
+    abs_expense = "abs_expense"     # Betrag ohne Vorzeichen, immer Ausgabe
+
+
+class MatchField(str, enum.Enum):
+    payee = "payee"
+    purpose = "purpose"
+
+
+class ImportStatus(str, enum.Enum):
+    committed = "committed"
+    undone = "undone"
+
+
 class User(Base):
     __tablename__ = "users"
 
@@ -273,6 +290,12 @@ class Transaction(Base):
     description: Mapped[str | None] = mapped_column(String(255), nullable=True)
     notes: Mapped[str | None] = mapped_column(Text, nullable=True)
 
+    # Import (Phase 4): Herkunft für Undo und Duplikaterkennung.
+    import_batch_id: Mapped[int | None] = mapped_column(
+        ForeignKey("import_batches.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    import_hash: Mapped[str | None] = mapped_column(String(64), nullable=True, index=True)
+
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)
     updated_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now, onupdate=_now)
 
@@ -394,3 +417,72 @@ class DashboardLayout(Base):
     # JSON-Array: [{i, type, x, y, w, h, props}]
     layout: Mapped[str] = mapped_column(Text, nullable=False, default="[]")
     updated_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now, onupdate=_now)
+
+
+# ---------------------------------------------------------------------------
+# Phase 4: CSV-Import (Templates, Batches für Undo, lernende Kategorie-Regeln)
+# ---------------------------------------------------------------------------
+
+
+class ImportTemplate(Base):
+    __tablename__ = "import_templates"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    owner_id: Mapped[int] = mapped_column(
+        ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    name: Mapped[str] = mapped_column(String(120), nullable=False)
+    delimiter: Mapped[str] = mapped_column(String(2), nullable=False, default=";")
+    decimal_sep: Mapped[str] = mapped_column(String(1), nullable=False, default=",")
+    date_format: Mapped[str] = mapped_column(String(32), nullable=False, default="%d.%m.%Y")
+    encoding: Mapped[str] = mapped_column(String(16), nullable=False, default="utf-8")
+    has_header: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
+    skip_rows: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    amount_mode: Mapped[AmountMode] = mapped_column(_enum(AmountMode), nullable=False, default=AmountMode.signed)
+    # JSON: Feld -> 0-basierter Spaltenindex (oder null). Felder: date, time,
+    # amount, debit, credit, currency, payee, purpose, counterparty_iban.
+    column_map: Mapped[str] = mapped_column(Text, nullable=False, default="{}")
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)
+
+
+class ImportBatch(Base):
+    __tablename__ = "import_batches"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    owner_id: Mapped[int] = mapped_column(
+        ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    account_id: Mapped[int] = mapped_column(
+        ForeignKey("accounts.id", ondelete="CASCADE"), nullable=False
+    )
+    template_id: Mapped[int | None] = mapped_column(
+        ForeignKey("import_templates.id", ondelete="SET NULL"), nullable=True
+    )
+    filename: Mapped[str] = mapped_column(String(255), nullable=False, default="")
+    row_count: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    imported_count: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    status: Mapped[ImportStatus] = mapped_column(_enum(ImportStatus), nullable=False, default=ImportStatus.committed)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)
+
+
+class CategorizationRule(Base):
+    """Lernende Regel: Empfänger/Zweck enthält Muster -> Kategorie (oder Transfer)."""
+
+    __tablename__ = "categorization_rules"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    owner_id: Mapped[int] = mapped_column(
+        ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    match_field: Mapped[MatchField] = mapped_column(_enum(MatchField), nullable=False, default=MatchField.payee)
+    pattern: Mapped[str] = mapped_column(String(255), nullable=False)  # normalisiert (lowercase)
+    category_id: Mapped[int | None] = mapped_column(
+        ForeignKey("categories.id", ondelete="CASCADE"), nullable=True
+    )
+    priority: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    hits: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)
+
+    __table_args__ = (
+        UniqueConstraint("owner_id", "match_field", "pattern", name="uq_rule_owner_field_pattern"),
+    )