fix(ci): remove cuda from ml default features, unblock CPU test-gate

The ml crate had `default = ["minimal-inference", "cuda"]` which pulled
in cudarc/candle-kernels requiring nvcc. CI test-gate runs on
ci-builder-cpu (no CUDA) so `cargo clippy --workspace` always panicked
with "Failed to execute nvcc: No such file or directory".

CUDA is now opt-in only — compile-and-train template already passes
`--features ml/cuda` explicitly for GPU builds.

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

crates/ml/Cargo.toml

@@ -15,7 +15,7 @@ categories.workspace = true
 [features]
 # MINIMAL features for HFT inference only - ALL HEAVY ML REMOVED
 # CUDA opt-in: service crates build on CPU nodes without nvcc
-default = ["minimal-inference", "cuda"]
+default = ["minimal-inference"]
 
 # PRODUCTION FEATURES - LIGHTWEIGHT ONLY
 minimal-inference = []  # Minimal inference with no optional deps