feat(capability-requests): add cross-domain capability catalog and request routing

Introduces a capability catalog (CUST-WP-0022) so domains can advertise what
they provide and agents can request capabilities from other domains with
auto-routing, lifecycle tracking, and task-unblocking on completion.

- New models: CapabilityCatalog, CapabilityRequest with full lifecycle
  (requested → accepted → in_progress → ready_for_review → completed/rejected/withdrawn)
- Migration i6d7e8f9a0b1: capability_catalog + capability_requests tables
- Router /capability-catalog and /capability-requests with accept/status endpoints
- 7 new MCP tools: register_capability, list_capabilities, request_capability,
  accept_capability_request, update_capability_request_status,
  list_capability_requests, get_capability_request
- StateSummary gains open_capability_requests count
- Dashboard: capability-requests.md page + docs/capabilities.md + docs/scope.md
- SCOPE.md: three seed capabilities documented (MCP registration, state tracking, SBOM)
- scope.template: Provided Capabilities section with example block
- scripts/ingest_capabilities.py + make ingest-capabilities[/-all] targets

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

api/models/__init__.py

@@ -15,6 +15,8 @@ from api.models.contribution import Contribution, ContributionType, Contribution
 from api.models.sbom_snapshot import SBOMSnapshot
 from api.models.sbom_entry import SBOMEntry, Ecosystem
 from api.models.agent_message import AgentMessage
+from api.models.capability_catalog import CapabilityCatalog
+from api.models.capability_request import CapabilityRequest
 
 __all__ = [
     "Base",
@@ -34,4 +36,6 @@ __all__ = [
     "SBOMSnapshot",
     "SBOMEntry", "Ecosystem",
     "AgentMessage",
+    "CapabilityCatalog",
+    "CapabilityRequest",
 ]