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>

crates/server/Cargo.toml

@@ -27,6 +27,7 @@ db = { path = "../db" }
 domain = { path = "../domain" }
 search = { path = "../search" }
 rpassword.workspace = true
+dotenvy.workspace = true
 memory-serve = { workspace = true, optional = true }
 
 [build-dependencies]