Move the host skills service into the skills extension (#36921)

## What changed

- Move host skill discovery, snapshot caching, and configuration handling from
  `codex-core-skills` to `codex-skills-extension`.
- Rename `SkillsService` and `SkillsLoadInput` to `HostSkillsService` and
  `HostSkillsLoadInput` to distinguish the host implementation from other skill
  providers.
- Keep shared loading primitives and skill outcome modeling in
  `codex-core-skills`.

GitOrigin-RevId: d81a21791d2ef8c066e157e7e538b8cb7ee4c24b

codex-rs/core/src/skills.rs

@@ -15,8 +15,6 @@ use tokio::sync::Mutex;
 
 pub use codex_core_skills::SkillError;
 pub use codex_core_skills::SkillLoadOutcome;
-pub use codex_core_skills::SkillsLoadInput;
-pub use codex_core_skills::SkillsService;
 pub use codex_core_skills::build_skill_name_counts;
 pub use codex_core_skills::config_rules;
 pub use codex_core_skills::detect_implicit_skill_invocation_for_command;
@@ -28,10 +26,12 @@ pub use codex_core_skills::injection::collect_explicit_skill_mentions;
 pub use codex_core_skills::loader;
 pub use codex_core_skills::model;
 pub use codex_core_skills::remote;
-pub use codex_core_skills::service;
 pub use codex_core_skills::system;
 pub use codex_skills::SkillMetadata;
 pub use codex_skills::SkillPolicy;
+pub use codex_skills_extension::HostSkillsLoadInput;
+pub use codex_skills_extension::HostSkillsService;
+pub use codex_skills_extension::bundled_skills_enabled_from_stack;
 
 #[derive(Debug, Default)]
 struct ImplicitSkillInvocations(Mutex<HashSet<String>>);
@@ -39,8 +39,8 @@ struct ImplicitSkillInvocations(Mutex<HashSet<String>>);
 pub(crate) fn skills_load_input_from_config(
     config: &Config,
     effective_skill_roots: Vec<PluginSkillRoot>,
-) -> SkillsLoadInput {
-    SkillsLoadInput::new(
+) -> HostSkillsLoadInput {
+    HostSkillsLoadInput::new(
         config.cwd.clone(),
         effective_skill_roots,
         config.config_layer_stack.clone(),