feat(keycloak): M4.3 — Admin API adapter + claim resolver

internal/keycloak Adapter (HTTPAdapter + Mock). POST /v1/tenants now provisions a KC organization + IT_ADMIN invite when admin_email is set; KC failures emit keycloak.provision_failed but don't roll back. POST /v1/internal/keycloak/claims resolves the current claim bundle for any (tenant_id|tenant_slug|user_attrs.*) lookup. Mock used in tests + when KEYCLOAK_ADMIN_URL is empty. HTTPAdapter tested against an in-process stub KC (httptest.Server).

Refs: M4.3

CHANGELOG.md

@@ -6,6 +6,7 @@ Generated section is appended on release tag via `git-cliff` (see `.gitea/workfl
 ## [Unreleased]
 
 ### Added
+- feat(keycloak): M4.3 — internal/keycloak adapter (Admin API: org create + IT_ADMIN invite + execute-actions-email + attribute sync). admin_email on POST /v1/tenants triggers KC provisioning; failures emit keycloak.provision_failed audit but don't roll back. POST /v1/internal/keycloak/claims resolves the current claim bundle for a tenant.
 - feat(api): M4.2 — full REST surface (tenants CRUD + lifecycle, catalog, entitlements, API keys w/ argon2 hashing, audit query). pgx-backed Postgres store; in-memory fallback when DATABASE_URL is empty. OpenAPI 3.1 spec at openapi.yaml with kin-openapi contract test.
 - feat(schema): M4.1 — golang-migrate migrations for tenants + tenant_projects + tenant_products + tenant_idp_config + api_keys + audit_log; cmd/migrate binary; testcontainers round-trip + seed + slug-constraint tests
 - feat(server): minimal Go service — /healthz + GET /v1/tenants/by-slug/:slug + GET /v1/tenants/:id with in-memory store seeded with the acme tenant