feat(T04): contact management + USt-IdNr. validation + contact UI

- Contact model: company, role (kaeufer/verkaeufer/beide), soft-delete
- ContactPerson model: 1:N relation with CASCADE delete
- USt-IdNr. validation: DE + 10 EU countries
- Contact CRUD: 7 API endpoints with RBAC, search/filter/paginate
- Frontend: ContactList, ContactForm, ContactDetail with EU/Inland toggle
- 73 backend tests (91% coverage), 20 frontend tests

backend/app/schemas/contact.py

@@ -0,0 +1,147 @@
+"""Pydantic schemas for contact-related request and response bodies."""
+
+import uuid
+from datetime import datetime
+from typing import Literal, Optional
+
+from pydantic import BaseModel, ConfigDict, EmailStr, Field, field_validator
+
+from app.utils.ust_validation import validate_vat_id
+
+
+ContactRole = Literal["kaeufer", "verkaeufer", "beide"]
+VatIdStatus = Literal["ungeprueft", "geprueft", "ungueltig", "manuell_bestaetigt"]
+
+
+class ContactPersonBase(BaseModel):
+    """Base contact person fields."""
+
+    name: str = Field(..., min_length=1, max_length=255)
+    function: Optional[str] = Field(None, max_length=100)
+    phone: Optional[str] = Field(None, max_length=50)
+    email: Optional[str] = Field(None, max_length=255)
+
+
+class ContactPersonCreate(ContactPersonBase):
+    """POST /api/v1/contacts/:id/persons request body."""
+    pass
+
+
+class ContactPersonResponse(ContactPersonBase):
+    """Contact person response schema."""
+
+    model_config = ConfigDict(from_attributes=True)
+
+    id: uuid.UUID
+    contact_id: uuid.UUID
+    created_at: Optional[datetime] = None
+
+
+class ContactBase(BaseModel):
+    """Base contact fields shared across schemas."""
+
+    company_name: str = Field(..., min_length=1, max_length=255)
+    legal_form: Optional[str] = Field(None, max_length=50)
+    address_street: Optional[str] = Field(None, max_length=255)
+    address_zip: Optional[str] = Field(None, max_length=10)
+    address_city: Optional[str] = Field(None, max_length=100)
+    address_country: str = Field("DE", min_length=2, max_length=2)
+    vat_id: Optional[str] = Field(None, max_length=20)
+    phone: Optional[str] = Field(None, max_length=50)
+    email: Optional[str] = Field(None, max_length=255)
+    website: Optional[str] = Field(None, max_length=255)
+    role: ContactRole
+    is_private: bool = False
+
+    @field_validator("vat_id")
+    @classmethod
+    def validate_vat_id_format(cls, v: str | None) -> str | None:
+        """Validate VAT ID format if provided."""
+        if v is None or v == "":
+            return None
+        if not validate_vat_id(v):
+            raise ValueError(f"Invalid VAT ID format: '{v}'")
+        return v.strip().upper().replace(" ", "")
+
+    @field_validator("address_country")
+    @classmethod
+    def validate_country_code(cls, v: str) -> str:
+        """Normalise country code to uppercase."""
+        return v.upper()
+
+
+class ContactCreate(ContactBase):
+    """POST /api/v1/contacts request body."""
+
+    contact_persons: list[ContactPersonCreate] = Field(
+        default_factory=list, description="Contact persons to create with the contact"
+    )
+
+
+class ContactUpdate(BaseModel):
+    """PUT /api/v1/contacts/:id request body (all fields optional)."""
+
+    company_name: Optional[str] = Field(None, min_length=1, max_length=255)
+    legal_form: Optional[str] = Field(None, max_length=50)
+    address_street: Optional[str] = Field(None, max_length=255)
+    address_zip: Optional[str] = Field(None, max_length=10)
+    address_city: Optional[str] = Field(None, max_length=100)
+    address_country: Optional[str] = Field(None, min_length=2, max_length=2)
+    vat_id: Optional[str] = Field(None, max_length=20)
+    phone: Optional[str] = Field(None, max_length=50)
+    email: Optional[str] = Field(None, max_length=255)
+    website: Optional[str] = Field(None, max_length=255)
+    role: Optional[ContactRole] = None
+    is_private: Optional[bool] = None
+
+    @field_validator("vat_id")
+    @classmethod
+    def validate_vat_id_format(cls, v: str | None) -> str | None:
+        """Validate VAT ID format if provided."""
+        if v is None or v == "":
+            return None
+        if not validate_vat_id(v):
+            raise ValueError(f"Invalid VAT ID format: '{v}'")
+        return v.strip().upper().replace(" ", "")
+
+    @field_validator("address_country")
+    @classmethod
+    def validate_country_code(cls, v: str | None) -> str | None:
+        """Normalise country code to uppercase."""
+        if v is not None:
+            return v.upper()
+        return v
+
+
+class ContactResponse(BaseModel):
+    """Contact response schema."""
+
+    model_config = ConfigDict(from_attributes=True)
+
+    id: uuid.UUID
+    company_name: str
+    legal_form: Optional[str] = None
+    address_street: Optional[str] = None
+    address_zip: Optional[str] = None
+    address_city: Optional[str] = None
+    address_country: str
+    vat_id: Optional[str] = None
+    phone: Optional[str] = None
+    email: Optional[str] = None
+    website: Optional[str] = None
+    role: str
+    vat_id_status: str = "ungeprueft"
+    is_private: bool = False
+    created_at: Optional[datetime] = None
+    updated_at: Optional[datetime] = None
+    deleted_at: Optional[datetime] = None
+    contact_persons: list[ContactPersonResponse] = Field(default_factory=list)
+
+
+class ContactListResponse(BaseModel):
+    """Paginated contact list response."""
+
+    items: list[ContactResponse]
+    total: int
+    page: int
+    page_size: int