Remove the codex-core-skills crate (#37505)

## What changed

- Move `SkillLoadOutcome` and its implicit-path indexing into
  `codex-skills-extension`.
- Import shared skill types directly from `codex-skills` and keep the skill
  prompt size limit with the extension renderer that uses it.
- Remove `codex-core-skills` from the Cargo workspace and dependent crates.

GitOrigin-RevId: 4e9e84909fa2f692bcc94af990bb4671affd776f

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

@@ -22,7 +22,6 @@ use tracing::instrument;
 use tracing::warn;
 
 use codex_config::SkillsConfig;
-use codex_core_skills::SkillLoadOutcome;
 use codex_skills::LoadedSkills;
 use codex_skills::SkillLoadFuture;
 use codex_skills::SkillRootLoadRequest;
@@ -31,6 +30,7 @@ use codex_skills::SkillRootSnapshots;
 use codex_skills::install_system_skills;
 
 use crate::HostSkillsSnapshot;
+use crate::SkillLoadOutcome;
 use crate::host_roots::resolve_skill_roots;
 use crate::loader::HostSkillRoot;
 use crate::loader::MAX_CONCURRENT_ROOT_SCANS;