Separate driver heading from pose estimation; fix auto pose init

[nlaverdure]

Summary

• Separates driver "forward" from pose estimation: The headingOffset concept is removed from Drive. Driver-relative heading is now purely a UI concern managed by DriveCommands.driverForwardDirection, while drive.getPose().getRotation() is the single source of truth for field-relative heading.
• Fixes auto pose initialization: Drive.setPose() now properly resets the pose estimator (was previously only resetting the heading offset), and sets a poseInitialized flag so getFieldRelativeHeading() returns null until the pose has field-relative meaning — preventing false vision yaw rejections at startup.
• Removes Drive.getHeading() / resetHeading(): All callers now use drive.getPose().getRotation() (field-relative) or drive.getRawGyroRotation() (characterization) as appropriate. Vision heading supplier updated from getRawGyroRotation to getFieldRelativeHeading.

Test plan

• Confirm field-relative drive works correctly after driver presses "reset forward"
• Confirm auto pose initialization sets pose correctly (robot faces expected direction at auto start)
• Confirm vision yaw consistency check does not false-reject at startup
• Confirm wheel radius characterization still functions correctly

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