feat(capability-requests): add routing dispute & reroute workflow (CUST-WP-0027)

Adds a structured dispute mechanism when capability request routing is wrong:
- New `routing_disputed` status with four DB columns (dispute_reason, disputed_by,
  dispute_suggested_domain, disputed_at) via Alembic migration m0h1i2j3k4l5
- POST /capability-requests/{id}/dispute — any party can flag misrouting with a reason
  and optional suggested domain; notifies custodian + current fulfilling domain
- POST /capability-requests/{id}/reroute — custodian re-routes to correct domain via
  catalog_entry_id or direct slug; appends audit trail to routing_note; resets to requested
- Two new MCP tools: dispute_capability_routing and reroute_capability_request
- Dashboard: amber disputed-banner at top of Summary, routing_disputed Kanban column,
  dispute details (reason, suggested domain, raised-by) shown on disputed cards

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/models/capability_request.py

@@ -66,6 +66,13 @@ class CapabilityRequest(Base, TimestampMixin):
 
     resolution_note: Mapped[str | None] = mapped_column(Text, nullable=True)
     routing_note: Mapped[str | None] = mapped_column(Text, nullable=True)
+
+    # Dispute fields (populated when status = routing_disputed)
+    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
     )