docs: add lib.rs doc comment to training_uploader

Add //! module-level doc comment to training_uploader/src/main.rs.
The other 6 crates (backtesting, ctrader-openapi, data, ml, risk,
trading_engine) already had doc comments and were skipped.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

crates/training_uploader/src/main.rs

@@ -1,5 +1,7 @@
 #![allow(unused_crate_dependencies)]
 
+//! K8s sidecar that uploads training artifacts to S3 and reports completion via gRPC.
+
 use std::collections::HashMap;
 use std::path::{Path, PathBuf};
 use std::time::{Duration, Instant};