Add hub-core package, docs, and State Hub integration scaffold

Extract the first reusable slice (models, schemas, routers, MCP, migrations)
from state-hub with INTENT/SCOPE, agent instructions, workplan, and aligned
inter_hub capability registry index.

hub_core/models/managed_repo.py

@@ -0,0 +1,37 @@
+import uuid
+
+from sqlalchemy import ForeignKey, String, Text
+from sqlalchemy.dialects.postgresql import JSONB, UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from hub_core.models.base import Base, TimestampMixin, new_uuid
+
+
+class ManagedRepo(Base, TimestampMixin):
+    __tablename__ = "managed_repos"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=new_uuid
+    )
+    domain_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("domains.id", ondelete="RESTRICT"),
+        nullable=False,
+        index=True,
+    )
+    slug: Mapped[str] = mapped_column(String(100), unique=True, nullable=False, index=True)
+    name: Mapped[str] = mapped_column(String(200), nullable=False)
+    local_path: Mapped[str | None] = mapped_column(Text, nullable=True)
+    host_paths: Mapped[dict] = mapped_column(JSONB, nullable=False, default=dict, server_default="{}")
+    remote_url: Mapped[str | None] = mapped_column(Text, nullable=True)
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    status: Mapped[str] = mapped_column(String(20), nullable=False, default="active")
+    git_fingerprint: Mapped[str | None] = mapped_column(String(40), nullable=True, index=True)
+
+    domain: Mapped["Domain"] = relationship(  # noqa: F821
+        "Domain", back_populates="repos", lazy="selectin"
+    )
+
+    @property
+    def domain_slug(self) -> str:
+        return self.domain.slug if self.domain is not None else ""