Move shared skill models into codex-skills (#34429)

## What changed

- Define and export skill metadata, policy, dependency, interface, and configuration rule types from `codex-skills`.
- Update core, plugin, and extension consumers to use the shared models while retaining compatibility re-exports from `codex-core-skills`.
- Share product-restriction handling between host and environment skill metadata.

## Testing

- Add unit coverage for default and explicit implicit-invocation and product policies.

GitOrigin-RevId: 9093469f8fff8e2d902dc9781235f64709827a87

codex-rs/ext/skills/src/catalog.rs

@@ -1,4 +1,4 @@
-use codex_core_skills::model::SkillDependencies;
+use codex_skills::SkillDependencies;
 use codex_utils_path_uri::PathUri;
 use std::sync::Arc;
 

codex-rs/ext/skills/src/provider/executor.rs

@@ -1,11 +1,11 @@
 use std::sync::Arc;
 
-use codex_core_skills::loader::EnvironmentSkillMetadata;
 use codex_core_skills::loader::load_environment_skills_from_discovery;
 use codex_core_skills::loader::load_environment_skills_from_root;
 use codex_exec_server::EnvironmentManager;
 use codex_protocol::capabilities::CapabilityRootLocation;
 use codex_protocol::protocol::Product;
+use codex_skills::EnvironmentSkillMetadata;
 use codex_utils_path_uri::PathConvention;
 
 use crate::catalog::SkillAuthority;

codex-rs/ext/skills/src/provider/host.rs

@@ -1,5 +1,5 @@
 use codex_core_skills::SkillLoadOutcome;
-use codex_core_skills::SkillMetadata;
+use codex_skills::SkillMetadata;
 
 use crate::catalog::SkillAuthority;
 use crate::catalog::SkillCatalog;