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  (requested → accepted → in_progress → ready_for_review → completed/rejected/withdrawn)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

dashboard/observablehq.config.js

@@ -19,6 +19,7 @@ export default {
   pages: [
     // ── Pages (Overview first, then alphabetical) ────────────────────────────
     { name: "Overview",      path: "/" },
+    { name: "Capabilities",  path: "/capability-requests" },
     { name: "Contributions", path: "/contributions" },
     { name: "Domains",       path: "/domains" },
     { name: "Goals",         path: "/goals" },
@@ -66,6 +67,7 @@ export default {
       collapsible: true,
       open: false,
       pages: [
+        { name: "Capabilities",              path: "/docs/capabilities" },
         { name: "Connecting to the Hub",    path: "/docs/connecting" },
         { name: "Contributions",            path: "/docs/contributions" },
         { name: "Decision Health",          path: "/docs/decisions-kpi" },
@@ -84,6 +86,7 @@ export default {
         { name: "Repo Integration",         path: "/docs/repo-integration" },
         { name: "Repos",                    path: "/docs/repos" },
         { name: "SBOM",                     path: "/docs/sbom" },
+        { name: "SCOPE.md",                 path: "/docs/scope" },
         { name: "Tasks",                    path: "/docs/tasks" },
         { name: "Technical Debt",           path: "/docs/debt" },
         { name: "Todo",                     path: "/docs/todo" },