v0.5.1: feat: add auto-instrumentation for Redis, PostgreSQL, and Tailscale

Wire redisotel and otelpgx libraries for automatic OTel tracing of
Redis commands and SQL queries, with configurable peer.service names
for Datadog service map visibility. Add manual spans around Tailscale
WhoIs, DNS lookup/forward, and dial calls.

New config fields:
- [redis] service_name (default: "redis")
- [listeners.postgres] service_name (default: listener name)