Velocity control PID shooter

[frbaker]

Summary

• Replace broken shooter PID with SPARK MAX built-in velocity control
• Add configurable PID gains and feedforward in Constants.h
• Add SmartDashboard telemetry for tuning (RPM, target, at-speed status)

Test plan

• Deploy to robot and verify shooter spins up to target RPM
• Tune PID gains using SmartDashboard feedback
• Verify AtTargetVelocity() returns true when at speed

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