feat(npm): restart stale tsmd on package upgrade

[tashian]

Summary

• Adds a postinstall script to the npm wrapper that SIGTERMs any running tsmd on darwin so the next tsm command picks up the new binary.
• Idempotent and side-effect-light: no respawn, no pidfile, no JSON-RPC dependency.
• Skips silently on non-darwin (e.g. Linux CI installing the wrapper).
• Handles cross-prefix upgrades (Homebrew → npm) via a permissive owned-pid pass.

Closes #5

Implementation notes

• Script is refactored into pure-ish functions (resolveTsmdPath, findRunningTsmdPids, stopPids, main) with injectable deps (requireResolve, execFileSync, process.kill) so node:test covers every branch without spawning real processes.
• if (require.main === module) main() keeps require() side-effect-free for the test harness.
• EPERM on kill (daemon owned by another user after a stray sudo) downgrades to a warning, never fails the install. ESRCH swallowed silently (race between pgrep and kill). Unknown error codes are warned but still non-fatal.
• package.json files lists scripts/postinstall.js explicitly so the test file (scripts/postinstall.test.js) is not shipped in the published tarball.
• npm/wrapper/README.md notes the upgrade behavior and the --ignore-scripts opt-out.
• RELEASING.md gets a one-liner about the postinstall.

Deferred

• T6 (CI smoke test step) is deferred. Per repo conventions for this PR I did not add a new GH Actions workflow file; extending ci.yml with a Node test step is a follow-up. The unit tests are runnable today via node --test npm/wrapper/scripts/postinstall.test.js.
• T7 (real npm install -g . smoke test) is deferred to manual verification by the maintainer, per the task constraints (do not mutate the user's global npm prefix from automation).

Test plan

• node --test npm/wrapper/scripts/postinstall.test.js passes (16/16)
• npm pack --dry-run from npm/wrapper/ includes scripts/postinstall.js and excludes the test file
• Manual on darwin: tsm status (spawn daemon) → cd npm/wrapper && npm install -g . → pgrep -fl tsmd empty → tsm status respawns