Slow acceleration ramp to ~2s (was 0.4s)

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

gear_sonic_deploy/src/g1/g1_deploy_onnx_ref/include/input_interface/gamepad_manager.hpp

@@ -709,7 +709,7 @@ class GamepadManager : public InputInterface {
           double normalized = std::min((planner_stick_magnitude_ - dead_zone_) / (1.0 - dead_zone_), 1.0);
           double target_speed = normalized * 0.8;  // 0.0 at dead zone edge, 0.8 at full stick
           // Rate-limit acceleration only (decel is instant)
-          constexpr double max_accel_per_frame = 0.01;  // ~0.4s ramp 0→0.8 at 200Hz
+          constexpr double max_accel_per_frame = 0.002;  // ~2s ramp 0→0.8 at 200Hz
           if (target_speed > smoothed_speed_) {
             smoothed_speed_ = std::min(target_speed, smoothed_speed_ + max_accel_per_frame);
           } else {