fix(action): install Claude Code only for Claude runtime

[tmustier]

Companion PR to issue #333
See writeup and evidence in the issue. I am more than happy to amend in particular to generalise, just let me know if you don't like implementation

Pi writeup below:

Summary

• Move Claude Code setup out of the composite action's unconditional pre-step and into the JS runtime setup path, after matched triggers have been resolved.
• This keeps the fix small: Claude Code is installed/found only when a matched trigger uses runtime = "claude"; Pi runtime runs skip Claude Code setup.

Detail

• Changes:
  • Remove the unconditional Claude Code install step from action.yml
  • Add a small action-layer runtime setup helper after matched triggers are resolved
  • Skip Claude Code setup for runtime = "pi"
  • For runtime = "claude", validate auth and install/find Claude Code on demand using the current install script/version/retry behaviour
• Context: see GitHub Action installs Claude Code even when resolved runtime is Pi #333 for the detailed motivation and evidence. In short, Pi-only action runs currently install Claude Code even though the Pi runtime does not use it, which is confusing and adds avoidable CI time.
• Tests
  • pnpm vitest run src/action/workflow/base.test.ts src/action/workflow/pr-workflow.test.ts src/action/workflow/schedule.test.ts src/action/triggers/executor.test.ts
  • pnpm typecheck
  • pnpm lint
  • pnpm build
  • End-to-end smoke test in a dummy repo: https://github.com/tmustier/warden-test/actions/runs/26031290149
    • Pi runtime invoked the model and asserted Claude Code was not installed
    • Claude runtime installed Claude Code, invoked the model, and asserted the executable exists

[dcramer]

Thanks! Totally missed this with the recent Pi changes. Will get a couple minor cleanups in and land this