feat(registry): complete ATLAS-WP-0002 T04 (canon mapping) + T01 (surface schema)

T04: add docs/canon-mapping.md mapping config-atlas concepts to InfoTechCanon
(itc-gov/data/devsecops/land/org/access/sec/tag) and sibling repos with
consume/reference/align/own ownership, plus gaps, validation hooks, and
extension candidates. Resolves the (planned) refs in PRD and ecosystem-boundaries.

T01: add schemas/surface-entry.schema.json (Draft 2020-12, additionalProperties
false to forbid inline values/secrets), docs/configuration-surface-schema.md
(fields, kind taxonomy, L0-L9 ordering, explicit merge rules), a validating seed
entry (surface.infotech.state-hub.api-config), and expand registry/README.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

registry/README.md

@@ -1,4 +1,20 @@
-# Capability Registry
+# Registry
+
+Markdown-first registry for config-atlas. Two entry families:
+
+- **Configuration surfaces** (`surfaces/`) — the atlas's core artifact. Each entry
+  maps a configuration surface (where it lives, owner, kind, scope, source links),
+  validated against [`../schemas/surface-entry.schema.json`](../schemas/surface-entry.schema.json).
+  See [`../docs/configuration-surface-schema.md`](../docs/configuration-surface-schema.md)
+  for the model and [`../docs/canon-mapping.md`](../docs/canon-mapping.md) for ITC alignment.
+  Index: `indexes/surfaces.yaml` (ATLAS-WP-0002-T03).
+- **Capabilities** (`capabilities/`) — capability index for reuse-surface federation
+  (below).
+
+Surfaces store the **map only** — never live configuration values, never secret
+values.
+
+## Capability Registry
 
 Markdown-first capability index for federation and reuse planning.