fix(install): link skills where codex looks

Codex 0.148 discovers skills under $CODEX_HOME/skills only, so every
skill in this repo was invisible to codex sessions — review sessions run
by a codex reviewer reported review-pr as an unavailable skill and fell
back to improvising a review.

Both installers now link each skill into ~/.codex/skills as well. The
nix module links one symlink per skill dir instead of recursive=true:
codex skips any skill whose SKILL.md is itself a symlink, which is what
a per-file link produces.

nix/home.nix

@@ -40,6 +40,22 @@ let
   repo = cfg.repoPath;
 
   mkEnable = what: lib.mkEnableOption "the ${what} user unit";
+
+  # Codex reads $CODEX_HOME/skills and nothing else -- ~/.agents/skills reaches
+  # pi and opencode but not codex, which is why codex review sessions reported
+  # review-pr as an unavailable skill. One symlink per skill dir rather than
+  # recursive=true: codex skips any skill whose SKILL.md is itself a symlink,
+  # which is exactly what a per-file link produces. Per-skill also leaves
+  # codex's own ~/.codex/skills/.system in place, which a whole-dir link would
+  # replace.
+  skillNames = builtins.attrNames (
+    lib.filterAttrs (_: type: type == "directory") (builtins.readDir "${agent-skills}/skills")
+  );
+  codexSkills = lib.listToAttrs (
+    map (name: lib.nameValuePair ".codex/skills/${name}" {
+      source = "${agent-skills}/skills/${name}";
+    }) skillNames
+  );
 in
 {
   options.programs.agentSkills = {
@@ -71,7 +87,7 @@ in
     weekReview.enable = mkEnable "weekly review timer";
   };
 
-  config.home.file = {
+  config.home.file = codexSkills // {
     ".claude/skills" = {
       source = "${agent-skills}/skills";
       recursive = true;