Feat: Add per-joint finger pose API

[1001Bits]

Summary

• Adds setHandPoseCustomJointPositions(tag, hand, values[15]) to the FRIK API for per-joint finger control
• Accepts 15 float values (3 joints per finger: proximal, medial, distal) instead of 5 per-finger values
• Enables mods to control each finger joint independently for more natural grip animations around objects
• API version bumped from 2 to 3, fully backward compatible

Motivation

The existing setHandPoseCustomFingerPositions duplicates a single value across all 3 joints of each finger. This works for simple poses but doesn't allow independent joint control needed for realistic object gripping (e.g. wrapping fingers around items of different sizes).

FRIK internally already supports per-joint values — setHandPoseOverride(), HAND_FINGERS_POINTING_POSE[15], and calculateHandPose() all work per-bone. This PR simply exposes that capability through the public API.

Changes

• FRIKApi.h: Bump FRIK_API_VERSION to 3, add setHandPoseCustomJointPositions function pointer
• FRIKApi.cpp: Add wrapper function + function table entry
• HandPose.h/cpp: Add setFingerJointPositions(isLeft, values[15]) internal function

Value ordering

Index 0-2:   Thumb   (proximal, medial, distal)
Index 3-5:   Index   (proximal, medial, distal)
Index 6-8:   Middle  (proximal, medial, distal)
Index 9-11:  Ring    (proximal, medial, distal)
Index 12-14: Pinky   (proximal, medial, distal)

Matches internal LEFT_HAND_FINGERS[] / RIGHT_HAND_FINGERS[] bone order. Values 0.0 = bent, 1.0 = straight.

Backward compatibility

New function pointer appended at end of FRIKApi struct. Existing v2 mods never access it. clearHandPose() works unchanged for both old and new API paths.