Hub-and-Spoke Umbau: Multi-Tenant Zentrale + Satellite-Agent

- Backend: Customer/Satellite Models, customer_id auf Server/Job/Audit
- Satellite-API: heartbeat, poll (atomares Claiming), logs, result,
  scan-result, health-report - Auth via X-Api-Key (SHA-256 gehasht)
- Job-Queue: pending/claimed/running/success/failed + Stale-Janitor
- Batch-Trigger: ein Job pro Server, Satellite arbeitet sequenziell ab
- Credentials bleiben lokal: nur symbolische credential_ref zentral
- Neues Paket satellite/: Pull-Loop, WinRM/SSH/CAU/Scanner, PyInstaller-tauglich
- Frontend: Kunden-Switcher, Satelliten-View, Polling statt WebSocket
- Entfernt: WebSocket/Socket.io, Redis, zentrale Credentials, JobRunner
- Docs: README/AGENTS/PROMPT auf neue Architektur aktualisiert

backend/app/models/customer.py

@@ -0,0 +1,36 @@
+"""Customer model - one per client site (tenant)."""
+
+from datetime import UTC, datetime
+
+from sqlalchemy import DateTime, String, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.core.database import Base
+
+
+class Customer(Base):
+    __tablename__ = "customers"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    name: Mapped[str] = mapped_column(String(255), unique=True, index=True)
+    slug: Mapped[str] = mapped_column(String(100), unique=True, index=True)
+    notes: Mapped[str | None] = mapped_column(Text, nullable=True)
+
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(UTC)
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(UTC),
+        onupdate=lambda: datetime.now(UTC),
+    )
+
+    satellites: Mapped[list["Satellite"]] = relationship(  # noqa: F821
+        back_populates="customer", cascade="all, delete-orphan"
+    )
+    servers: Mapped[list["Server"]] = relationship(  # noqa: F821
+        back_populates="customer", cascade="all, delete-orphan"
+    )
+    jobs: Mapped[list["UpdateJob"]] = relationship(  # noqa: F821
+        back_populates="customer", cascade="all, delete-orphan"
+    )