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  (requested → accepted → in_progress → ready_for_review → completed/rejected/withdrawn)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/routers/state.py

@@ -6,6 +6,7 @@ from sqlalchemy import func, select, text
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from api.database import get_session, engine
+from api.models.capability_request import CapabilityRequest
 from api.models.contribution import Contribution, ContributionStatus, ContributionType
 from api.models.decision import Decision, DecisionStatus, DecisionType
 from api.models.domain import Domain
@@ -204,6 +205,13 @@ async def get_summary(session: AsyncSession = Depends(get_session)) -> StateSumm
         if lic and any(pat in lic.upper() for pat in _COPYLEFT_PATS)
     )
 
+    # Open capability requests (non-terminal statuses)
+    open_cap_req_count = (await session.execute(
+        select(func.count()).select_from(CapabilityRequest).where(
+            CapabilityRequest.status.in_(["requested", "accepted", "in_progress", "ready_for_review"])
+        )
+    )).scalar() or 0
+
     return StateSummary(
         generated_at=datetime.now(tz=timezone.utc),
         totals=totals,
@@ -215,6 +223,7 @@ async def get_summary(session: AsyncSession = Depends(get_session)) -> StateSumm
         domains=domain_summaries,
         contribution_counts=contribution_counts,
         licence_risk_count=licence_risk_count,
+        open_capability_requests=open_cap_req_count,
         open_workstreams=[
             WorkstreamWithDeps(
                 **WorkstreamRead.model_validate(w).model_dump(),