fix: emit migration warning before tracing subscriber is initialised

Config::load fires before init_logging in the normal serve path, so the
tracing::warn! in load_json_and_migrate was silently dropped - the
subscriber didn't exist yet. Fix by calling init_logging("warn") before
Config::load so the migration notice is visible. The second init_logging
call with config.log_level is a harmless no-op (try_init semantics);
RUST_LOG is still respected because EnvFilter checks the env var first,
and "warn" is already the compiled default for log_level anyway

this adds no overhead, the subscriber is registered once; the second call is a no-op.

Author: CaptainMirage

src/main.rs

@@ -201,6 +201,7 @@ async fn main() -> ExitCode {
     }
 
     let config_path = mhrv_rs::data_dir::resolve_config_path(args.config_path.as_deref());
+    init_logging("warn"); // boot-time logging so migration warning is visible
     let config = match Config::load(&config_path) {
         Ok(c) => c,
         Err(e) => {