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/capability_request.py

@@ -0,0 +1,76 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, 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 CapabilityRequest(Base, TimestampMixin):
+    __tablename__ = "capability_requests"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=new_uuid
+    )
+    title: Mapped[str] = mapped_column(String(500), nullable=False)
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    capability_type: Mapped[str] = mapped_column(String(50), nullable=False)
+    priority: Mapped[str] = mapped_column(
+        String(20), nullable=False, default="medium", server_default="medium"
+    )
+    status: Mapped[str] = mapped_column(
+        String(20), nullable=False, default="requested", server_default="requested"
+    )
+
+    requesting_domain_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("domains.id", ondelete="RESTRICT"),
+        nullable=False,
+        index=True,
+    )
+    requesting_agent: Mapped[str] = mapped_column(String(100), nullable=False)
+    request_context: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
+
+    fulfilling_domain_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("domains.id", ondelete="SET NULL"),
+        nullable=True,
+        index=True,
+    )
+    fulfilling_agent: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    fulfillment_context: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
+
+    catalog_entry_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("capability_catalog.id", ondelete="SET NULL"),
+        nullable=True,
+    )
+
+    resolution_note: Mapped[str | None] = mapped_column(Text, nullable=True)
+    routing_note: Mapped[str | None] = mapped_column(Text, nullable=True)
+    dispute_reason: Mapped[str | None] = mapped_column(Text, nullable=True)
+    disputed_by: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    dispute_suggested_domain: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    disputed_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+    accepted_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+    completed_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+
+    requesting_domain: Mapped["Domain"] = relationship(  # noqa: F821
+        "Domain", foreign_keys=[requesting_domain_id], lazy="selectin"
+    )
+    fulfilling_domain: Mapped["Domain | None"] = relationship(  # noqa: F821
+        "Domain", foreign_keys=[fulfilling_domain_id], lazy="selectin"
+    )
+    catalog_entry: Mapped["CapabilityCatalog | None"] = relationship(  # noqa: F821
+        "CapabilityCatalog", lazy="selectin"
+    )
+
+    @property
+    def requesting_domain_slug(self) -> str:
+        return self.requesting_domain.slug if self.requesting_domain else ""
+
+    @property
+    def fulfilling_domain_slug(self) -> str | None:
+        return self.fulfilling_domain.slug if self.fulfilling_domain else None