Add capability registry scaffold and seed entries from reuse-surface

Bootstrap registry/indexes/capabilities.yaml and migrate helix_forge
capability entries owned by this repository for federation publishing.

registry/indexes/capabilities.yaml

@@ -0,0 +1,34 @@
+version: 1
+updated: '2026-06-16'
+domain: helix_forge
+capabilities:
+- id: capability.identity.subject-resolution
+  name: Identity Subject Resolution
+  summary: Resolve who or what is acting by mapping principals, accounts, actors,
+    and identifiers to a stable subject model.
+  vector: D3 / A0 / C1 / R0
+  domain: helix_forge
+  status: draft
+  owner: identity-canon
+  path: registry/capabilities/capability.identity.subject-resolution.md
+  tags:
+  - identity
+  - subject
+  - architecture
+  consumption_modes:
+  - informational
+- id: capability.identity.vocabulary-canonicalize
+  name: Identity Vocabulary Canonicalization
+  summary: Define an implementation-neutral vocabulary for identity-related concepts
+    across overlapping domains.
+  vector: D4 / A0 / C2 / R0
+  domain: helix_forge
+  status: draft
+  owner: identity-canon
+  path: registry/capabilities/capability.identity.vocabulary-canonicalize.md
+  tags:
+  - identity
+  - terminology
+  - research
+  consumption_modes:
+  - informational