Centralize skill invocation helpers in codex-skills (#37174)

## What changed

- Move tool mention parsing, skill-name counting, and implicit invocation detection into `codex-skills` and expose them through its public API.
- Decouple implicit invocation detection from `SkillLoadOutcome` with an `ImplicitSkillLookup` trait, while preserving the existing `core-skills` interface through re-exports.
- Cover remote plugin attribution for both implicit `SKILL.md` reads and skill script runs.

GitOrigin-RevId: f3da85c9821868638ccfd2fc2e01e0869d2fd437

codex-rs/skills/src/lib.rs

@@ -1,11 +1,24 @@
 mod interface;
+mod invocation;
+mod mentions;
 mod model;
+mod name_counts;
 mod parser;
 mod policy;
 
 pub use interface::SkillInterfaceAssetPolicy;
 pub use interface::SkillInterfaceFile;
 pub use interface::resolve_skill_interface;
+pub use invocation::ImplicitSkillLookup;
+pub use invocation::detect_implicit_skill_invocation_for_command;
+pub use mentions::ToolMentionKind;
+pub use mentions::ToolMentions;
+pub use mentions::app_id_from_path;
+pub use mentions::extract_tool_mentions;
+pub use mentions::extract_tool_mentions_with_sigil;
+pub use mentions::normalize_skill_path;
+pub use mentions::plugin_config_name_from_path;
+pub use mentions::tool_kind_for_path;
 pub use model::EnvironmentSkillMetadata;
 pub use model::SkillConfigRule;
 pub use model::SkillConfigRuleSelector;
@@ -15,6 +28,7 @@ pub use model::SkillInterface;
 pub use model::SkillMetadata;
 pub use model::SkillPolicy;
 pub use model::SkillToolDependency;
+pub use name_counts::build_skill_name_counts;
 pub use parser::ParsedSkillFrontmatter;
 pub use parser::SkillParseError;
 pub use parser::parse_skill_frontmatter_metadata;