`local` no longer makes sense as a configurable environment — the local
sandbox provider ignores image/resources/network/lifecycle/volumes. Stop
seeding it as an editable TOML file and stop offering it as a creatable
provider in the UI form.
Instead the server synthesizes a reserved, in-memory `local` environment
only when `server.sandbox.providers.local.enabled`. It is never persisted
and cannot be created, replaced, or deleted (409). Provider-enablement is
already enforced at run create/preflight/start, so the synthetic `local`
just needs to exist in the store catalog when enabled.
- fabro-environment: drop `local` from disk seeds; thread `local_enabled`
into load_or_seed and inject a synthetic `local`; ignore any stale
`local.toml`; reject create/replace/delete of `local` with a new
Reserved error. seeded_catalog_layer keeps `local` for CLI validation.
- fabro-server: pass local.enabled into the store; map Reserved -> 409.
- web: form provider dropdown excludes local; the `local` row is
read-only (no Edit/Delete) with a reserved tag.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>