feat(server): load .env via dotenvy on startup

The binary now reads a .env file itself (dotenvy::dotenv() at the top of main),
so 'cargo run -p server' / the release binary pick up config without relying on
just's 'set dotenv-load'. Missing .env is a no-op.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -2077,6 +2077,7 @@ dependencies = [
  "clap",
  "db",
  "domain",
+ "dotenvy",
  "http-body-util",
  "memory-serve",
  "reqwest",