D-030 Layer 3: E2E test spawns the Rust server binary, connects via LocalBridge, sends a batched MoveNorth input, and verifies the player moved to (16.5, 15.5). Also adds batch encoding roundtrip tests, framed batch test, and Player entity fixture decode test. 43/43 pass. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>