drop stale ENABLE_REGISTRY_VALIDATION env var

[MsfPablo]

What

Removes AGENT_REGISTRY_ENABLE_REGISTRY_VALIDATION and config.enableRegistryValidation everywhere they're rendered as if they were an active runtime knob.

Why

Issue #566 — the OSS Helm chart and the local docker-compose both still render this env var, but the current server config no longer reads it. The actual validation path goes through types.AppOptions.RegistryValidator and the v1alpha1 resource handlers. The chart value looks like a working toggle when it is dead surface.

The reporter's suggested cleanup, applied here:

• Remove config.enableRegistryValidation from the chart values.yaml, the regenerated README.md, the configmap.yaml template, and the chart unit test that asserts on it.
• Drop the matching AGENT_REGISTRY_ENABLE_REGISTRY_VALIDATION line from the local docker/docker-compose.yml.
• Drop the matching # Registry Validation block from .env.example.

Changes

 .env.example                                   | 4 ----
 charts/agentregistry/README.md                 | 1 -
 charts/agentregistry/templates/configmap.yaml  | 1 -
 charts/agentregistry/tests/configmap_test.yaml | 6 ------
 charts/agentregistry/values.yaml               | 2 --
 docker/docker-compose.yml                      | 2 --
 6 files changed, 16 deletions(-)

Test plan

• go build ./... clean
• make charts-docs regenerates the README with the table row removed (no config.enableRegistryValidation entry in the Parameters table)
• grep -rn 'ENABLE_REGISTRY_VALIDATION\|enableRegistryValidation' over *.go *.yaml *.yml *.md *.example *.tpl returns no hits
• helm-unittest is not installed in this environment; the chart unit test that asserted on the removed env var was deleted alongside it (it would otherwise fail on this PR). Operators with helm-unittest should run helm unittest charts/agentregistry locally.

Notes

• Registry validation is now controlled solely by types.AppOptions.RegistryValidator (per the reporter's guidance). Any deployment that still sets AGENT_REGISTRY_ENABLE_REGISTRY_VALIDATION will see it ignored — no behavior change for callers already on the new validator path.
• The other env vars on the configmap (AGENT_REGISTRY_SERVER_ADDRESS, AGENT_REGISTRY_MCP_PORT) are untouched.
• Disclosed: this PR was authored with LLM assistance under the MsfPablo persona.