Add native celld configuration and KV store providers #437

Scope

Track the native store-provider implementation in #422, stacked on the AWS/native-store infrastructure in #414.

• Immutable celld configuration snapshots and live celld KV through the embedded scoped API.
• Independent default-off config/KV features, per-ID native bindings and separate AWS/celld credentials and preparation budgets.
• Bounded transport, redacted failures, startup ordering, CLI structural validation and generated-consumer support.
• Tests, operator documentation and explicit opt-in local-service acceptance.

This is store-provider work. It does not implement the celld HTTP runtime adapter tracked by #421.

Acceptance

• Review and merge Add native celld config and KV store providers #422 after integrating its prerequisite stack.
• Pass relevant provider, native startup, feature-isolation and generated-consumer checks against the revision being merged.
• Resolve or explicitly retain the documented dependency on the companion celld scoped API, with reproducible service acceptance and an available reviewed artifact.
• Preserve the PR's documented proof limits. Fleet forwarding, reload/failover, production isolation, replication/storage acceptance and sustained stress are not certified by local tests.

Detailed verification and remaining draft gates are recorded in #422. Related native-provider work is tracked in #410; portable store traits and HTTP runtime ownership remain unchanged.