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/core-plugins/src/loader.rs

@@ -26,8 +26,6 @@ use codex_config::types::PluginMcpServerConfig;
 use codex_connectors::parse_plugin_app_config;
 use codex_connectors::parse_plugin_app_config_value;
 use codex_core_skills::PluginSkillSnapshots;
-use codex_core_skills::SkillMetadata;
-use codex_core_skills::config_rules::SkillConfigRules;
 use codex_core_skills::config_rules::resolve_disabled_skill_paths;
 use codex_core_skills::config_rules::skill_config_rules_from_stack;
 use codex_core_skills::loader::SkillRoot;
@@ -44,6 +42,8 @@ use codex_plugin::app_connector_ids_from_declarations;
 use codex_protocol::auth::AuthMode;
 use codex_protocol::protocol::Product;
 use codex_protocol::protocol::SkillScope;
+use codex_skills::SkillConfigRules;
+use codex_skills::SkillMetadata;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use codex_utils_plugins::find_plugin_manifest_path;
 use serde_json::Value as JsonValue;