Use AbsolutePathBuf in skill loading and codex_home (#17407)

Helps with FS migration later

codex-rs/Cargo.lock

@@ -2351,6 +2351,7 @@ dependencies = [
  "codex-plugin",
  "codex-protocol",
  "codex-rmcp-client",
+ "codex-utils-absolute-path",
  "codex-utils-plugins",
  "futures",
  "pretty_assertions",
@@ -2989,6 +2990,7 @@ version = "0.0.0"
 name = "codex-utils-home-dir"
 version = "0.0.0"
 dependencies = [
+ "codex-utils-absolute-path",
  "dirs",
  "pretty_assertions",
  "tempfile",