Release v0.1.5

Release v0.1.5: Unix socket support + deps refresh

Features:
- New SOCKET_PATH env var. When set, the server binds a Unix domain
  socket (chmod 0660) instead of a TCP port. Takes precedence over PORT.
  Lets a reverse proxy (cloudflared, nginx, …) handle network exposure
  without opening a port on the host.
- README documents the systemd unit (RuntimeDirectory, UMask) and
  example ingress configs for cloudflared and nginx.

Dependencies:
- serde_yaml (archived) → serde_yml 0.0.12 (maintained fork, same API)
- rand 0.8 → 0.9 (rand::thread_rng() renamed to rand::rng())
- actix-web 4.5 → 4.13, env_logger 0.11.3 → 0.11.10, plus minor bumps
- Drop unused 'small_rng' feature flag from rand
- Pin to minor versions in Cargo.toml so patches roll in via cargo update

Cleanup (clippy strict, all-targets -D warnings):
- .split('/').last() → .next_back()
- !x.is_ok() → x.is_err()
- .expect(format!(...).as_str()) → .unwrap_or_else(|e| panic!(...)),
  preserving the underlying error in the message
- Reap the child process after the stdout/stderr threads join, so it
  doesn't linger as a zombie (clippy::zombie_processes)