refactor(skills): migrate skills to agent-skills-nix (#137)

* refactor(skills): migrate skills to agent-skills-nix

- Remove local skills directory from git tracking
- Add agent-skills-nix and StackOneHQ/skills as flake inputs
- Configure devShell to auto-install skills via symlink-tree
- Update .gitignore to exclude Nix-managed skill directories
- Update CLAUDE.md to document the new skills management approach

Skills are now sourced from StackOneHQ/skills repository and
automatically installed when entering `nix develop`.

* chore(skills): add .agents/skills directory for Codex compatibility

Add .agents/skills as a target for agent-skills-nix alongside .claude/skills.
This directory is used by Codex and other coding agents.

Author: ryoppippi

.claude/skills/just-commands/SKILL.md

@@ -17,3 +17,7 @@ build/
 
 # Git hooks (managed by Nix)
 .pre-commit-config.yaml
+
+# Agent skills (managed by Nix via agent-skills-nix)
+.claude/skills
+.agents/skills

.claude/skills/release-please/SKILL.md

@@ -5,7 +5,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 ## Rules and Skills Structure
 
 - **Rules** (`.claude/rules/`): Automatically loaded based on file paths. Source of truth for project conventions.
-- **Skills** (`.claude/skills/`): Manually invoked for specific integrations.
+- **Skills** (`.claude/skills/`): Managed by Nix via [agent-skills-nix](https://github.com/Kyure-A/agent-skills-nix). Skills are sourced from [StackOneHQ/skills](https://github.com/StackOneHQ/skills) and installed automatically when entering `nix develop`.
 - **Cursor rules** (`.cursor/rules/`): Symlinks to `.claude/rules/` for consistency.
 
 ## Available Skills

.gitignore

@@ -6,15 +6,47 @@
     flake-parts.url = "github:hercules-ci/flake-parts";
     git-hooks.url = "github:cachix/git-hooks.nix";
     treefmt-nix.url = "github:numtide/treefmt-nix";
+
+    # Agent skills management
+    agent-skills.url = "github:Kyure-A/agent-skills-nix";
+    agent-skills.inputs.nixpkgs.follows = "nixpkgs";
+
+    # StackOne skills repository (non-flake)
+    stackone-skills.url = "github:StackOneHQ/skills";
+    stackone-skills.flake = false;
   };
 
   outputs =
     inputs@{
       flake-parts,
       git-hooks,
       treefmt-nix,
+      agent-skills,
+      stackone-skills,
       ...
     }:
+    let
+      # Agent skills configuration (outside flake-parts for access to inputs)
+      agentLib = agent-skills.lib.agent-skills;
+      sources = {
+        stackone = {
+          path = stackone-skills;
+          subdir = ".";
+        };
+      };
+      catalog = agentLib.discoverCatalog sources;
+      allowlist = agentLib.allowlistFor {
+        inherit catalog sources;
+        enable = [
+          "just-commands"
+          "release-please"
+        ];
+      };
+      selection = agentLib.selectSkills {
+        inherit catalog allowlist sources;
+        skills = { };
+      };
+    in
     flake-parts.lib.mkFlake { inherit inputs; } {
       systems = [
         "x86_64-linux"
@@ -34,6 +66,7 @@
             };
             settings.formatter.oxfmt = {
               command = "${pkgs.oxfmt}/bin/oxfmt";
+              options = [ "--no-error-on-unmatched-pattern" ];
               includes = [
                 "*.md"
                 "*.yml"
@@ -76,6 +109,23 @@
               };
             };
           };
+
+          # Agent skills bundle and targets
+          bundle = agentLib.mkBundle { inherit pkgs selection; };
+          localTargets = {
+            claude = {
+              dest = ".claude/skills";
+              structure = "symlink-tree";
+              enable = true;
+              systems = [ ];
+            };
+            agents = {
+              dest = ".agents/skills";
+              structure = "symlink-tree";
+              enable = true;
+              systems = [ ];
+            };
+          };
         in
         {
           formatter = treefmtEval.config.build.wrapper;
@@ -101,19 +151,23 @@
 
               # Initialize git submodules if not already done
               if [ -f .gitmodules ] && [ ! -f vendor/stackone-ai-node/package.json ]; then
-                echo "📦 Initializing git submodules..."
+                echo "Initializing git submodules..."
                 git submodule update --init --recursive
               fi
 
               # Install Python dependencies only if .venv is missing or uv.lock is newer
               if [ ! -d .venv ] || [ uv.lock -nt .venv ]; then
-                echo "📦 Installing Python dependencies..."
+                echo "Installing Python dependencies..."
                 uv sync --all-extras --locked
               fi
 
               # Install git hooks
               ${pre-commit-check.shellHook}
-            '';
+            ''
+            + agentLib.mkShellHook {
+              inherit pkgs bundle;
+              targets = localTargets;
+            };
           };
         };
     };