Validate internal framework-docker slot collisions during mesh docker injection.

[nhynes]

Current issue:

• In compiler/src/targets/mesh/docker_compose/framework_docker_injection.rs, the pass uses the fixed slot name
  __amber_internal_framework_docker.
• If a component already has a slot with that name, the code reuses it without checking capability kind.
• That can silently repurpose a user-authored slot and create confusing routing behavior.

Expected behavior:

• If the slot already exists, require it to be kind: docker; otherwise fail compilation with a clear error (component moniker,
  slot name, expected vs actual kind).
• If it does not exist, create the injected internal docker slot.
• (Alternative acceptable direction: generate a guaranteed-unique hidden slot name per component.)

Test coverage to add:

• Existing slot with reserved name and non-docker kind -> compile error.
• Existing slot with reserved name and docker kind -> no error, safe reuse.
• No existing slot -> injected slot created and wired correctly.