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  (requested → accepted → in_progress → ready_for_review → completed/rejected/withdrawn)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>

SCOPE.md

@@ -97,6 +97,31 @@ The Custodian is both an **operational system** (State Hub: PostgreSQL + FastAPI
 
 ---
 
+## Provided Capabilities
+
+```capability
+type: api
+title: MCP tool registration
+description: Register and expose new MCP tools to all Claude Code sessions via the state-hub server.
+keywords: [mcp, tool, api, registration, server]
+```
+
+```capability
+type: data
+title: Cross-domain state tracking
+description: Track workstreams, tasks, decisions, and progress events across all six project domains.
+keywords: [state, tracking, workstream, task, decision, progress]
+```
+
+```capability
+type: api
+title: SBOM and licence reporting
+description: Ingest lockfiles from any repo and provide aggregated SBOM and copyleft licence risk reports.
+keywords: [sbom, licence, license, dependency, lockfile, copyleft]
+```
+
+---
+
 ## Notes
 
 Dependency order for domain sequencing: Railiance → Markitect → Coulomb.social → Personhood/Foerster → Custodian. The consistency checker (`make fix-consistency REPO=the-custodian`) must be run after any workplan changes to keep the dashboard accurate.