Unify Kimi/Codex skill naming and migrate legacy dotted Kimi dirs (#1971)

* fix: unify hyphenated skills and migrate legacy kimi dotted dirs

* fix: preserve legacy kimi dotted preset skill overrides

* fix: migrate kimi legacy dotted skills without ai-skills flag

* fix: harden kimi migration and cache hook init options

* fix: apply kimi preset skill overrides without ai-skills flag

* fix: keep sequential branch numbering beyond 999

* test: align kimi scaffold skill path with hyphen naming

* chore: align hook typing and preset skill comment

* fix: restore AGENT_SKILLS_DIR_OVERRIDES compatibility export

* refactor: remove AGENT_SKILLS_DIR_OVERRIDES and update callers

* fix(ps1): support sequential branch numbers above 999

* fix: resolve preset skill placeholders for skills agents

* Fix legacy kimi migration safety and preset skill dir checks

* Harden TOML rendering and consolidate preset skill restore parsing

* Fix PowerShell overflow and hook message fallback for empty invocations

* Restore preset skills from extensions

* Refine preset skill restore helpers

* Harden skill path and preset checks

* Guard non-dict init options

* Avoid deleting unmanaged preset skill dirs

* Unify extension skill naming with hooks

* Harden extension native skill registration

* Normalize preset skill titles