Add --warmup: keep the main worktree fresh, make setup wait on it

[EasterPeanut]

New worktrees are seeded from the main worktree's build caches and databases, so they're only as fresh as main. A stale main means every new worktree starts with an outdated branch, cold caches, and an unmigrated database — and creating a worktree while main is mid-compile can copy a half-built cache.

What this adds

werksfeer --warmup [--force]

Updates the main worktree (can be triggered from cron, launchd, or shell startup):

1. Checks out the default branch (from origin/HEAD; override with [warmup] branch) and pulls with --ff-only. Refuses to touch a main worktree with uncommitted tracked changes; untracked files are fine.
2. Runs a per-project-type refresh chain (override with [warmup] command):

Type	Command
Rails	bundle install && bin/rails db:prepare
Elixir	mix deps.get && mix compile && mix ecto.migrate (+ node package install if package.json exists)
Python	uv sync / pipenv install / pip install -r requirements.txt
Node	npm ci / yarn / pnpm / bun

Optional [warmup] min_interval (minutes) throttles repeated triggers; --force overrides.

Setup waits on a running warmup

While a warmup runs it holds a per-project lock under ~/.local/share/werksfeer/warmup/. The normal setup flow now waits on that lock before copying from main (configurable [warmup] wait_timeout, default 1800s), so a new worktree never copies a half-built _build/.bundle. Stale locks from crashed runs are detected by PID and removed automatically. Projects that never run --warmup are unaffected — no lock ever exists, the wait is a no-op.

Testing

• bash -n clean
• Smoke-tested with a scratch repo: --warmup pulls and runs the configured command; second run within min_interval skips; --force overrides
• Integration: created a worktree while a warmup was sleeping — setup printed Warmup in progress on main worktree, waiting..., blocked until the lock cleared, then completed; lock dir removed afterwards
• Stale-lock path: lock with a dead PID is removed and setup continues

🤖 Generated with Claude Code

[EasterPeanut]

Not merging this one yet, want to look at it with colleague when he returns from his vacation.