## Why
Hosted skills introduced by #27388 use opaque `skill://` resource
identifiers, but the skills catalog rendered every locator as a `file`
and told the model that every skill body lived on disk. That can send
the model toward filesystem tools for a resource that must instead be
read through its owning authority.
The catalog should describe how each source is accessed without changing
the underlying discovery or invocation behavior.
## What changed
- Render host skills as `file`, executor-owned skills as `environment
resource`, orchestrator-owned skills as `orchestrator resource`, and
custom-provider skills as `custom resource`.
- Update the shared no-alias guidance to describe source locators rather
than assuming every skill is stored on the host filesystem.
- Direct orchestrator resources through `skills.list` and `skills.read`,
and explicitly tell the model not to treat `skill://` identifiers as
filesystem paths.
- Preserve the existing filesystem and alias behavior for local skills.
## Scope
This PR changes only model-visible catalog rendering and guidance. It
does not change skill discovery, selection, prompt injection, provider
routing, catalog caching or refresh behavior, resource validation, or
the `skills.*` tool contract.
## Verification
- Extended skills-extension coverage for host-file and executor-resource
labels.
- Extended the no-executor app-server flow to assert
orchestrator-resource wording and non-filesystem guidance.
jif
4322e01d2b