chore: using mise to manage node versions and tasks (#44)

* add mise for Node.js version management

Replace ad-hoc Node version pinning with mise (mise.toml + mise.lock).
This ensures all contributors and CI use the same Node LTS version.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* expand mise with env loading, PATH management, and task runner

- [env] _.file loads .env files for local API keys (replaces dotenv)
- [env] _.path adds node_modules/.bin to PATH for direct tool access
- [tasks] mirrors npm scripts with sources/outputs for file-based caching
- eval tasks for running LLM evaluations via mise run
- update AGENTS.md and CONTRIBUTING.md to use mise run commands

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

mise.toml

@@ -0,0 +1,61 @@
+[settings]
+experimental = true
+lockfile = true
+
+[tools]
+node = "lts"
+
+[env]
+_.path = ["{{config_root}}/node_modules/.bin"]
+_.file = [".env", "packages/evals/.env"]
+
+# ── Root tasks ────────────────────────────────────────────────────────
+
+[tasks.install]
+description = "Install all dependencies"
+run = "npm install && npm --prefix packages/skills-build install && npm --prefix packages/evals install"
+sources = ["package.json", "packages/skills-build/package.json", "packages/evals/package.json"]
+outputs = ["node_modules/.package-lock.json"]
+
+[tasks.validate]
+description = "Validate all skills"
+run = "npm --prefix packages/skills-build run validate"
+sources = ["skills/**/SKILL.md", "skills/**/references/**"]
+
+[tasks.build]
+description = "Build all skills"
+run = "npm --prefix packages/skills-build run build"
+sources = ["skills/**/SKILL.md", "skills/**/references/**", "packages/skills-build/src/**"]
+outputs = ["skills/**/AGENTS.md"]
+
+[tasks.check]
+description = "Format and lint (auto-fix)"
+run = "biome check --write ."
+sources = ["**/*.ts", "**/*.js", "**/*.json", "biome.json"]
+
+[tasks."ci:check"]
+description = "CI format and lint check"
+run = "biome ci ."
+sources = ["**/*.ts", "**/*.js", "**/*.json", "biome.json"]
+
+[tasks.test]
+description = "Run tests"
+run = "vitest run"
+sources = ["test/**", "skills/**"]
+
+# ── Eval tasks ────────────────────────────────────────────────────────
+
+[tasks.eval]
+description = "Run all evals"
+run = "tsx packages/evals/src/cli.ts"
+sources = ["packages/evals/src/**", "skills/**/references/**"]
+
+[tasks."eval:code-fix"]
+description = "Run code-fix evals"
+run = "tsx packages/evals/src/cli.ts --type code-fix"
+sources = ["packages/evals/src/**", "skills/**/references/**"]
+
+[tasks."eval:workflow"]
+description = "Run workflow evals"
+run = "tsx packages/evals/src/cli.ts --type workflow"
+sources = ["packages/evals/src/**", "skills/**/references/**"]