EchoXR-Hands-v0.3.0

EchoXR Hands 0.3.0: hand tracking as its own repository

Per-finger hand tracking for Echo VR, moved out of heisthecat31/EchoXR:
the plugin, the finger bridge, the settings window, default settings and
test tools. Builds on its own (build.bat), and tools/make_release.py
makes EchoXR-Hands-v<VERSION>.zip, the asset EchoXR.exe downloads to
install and update hand tracking. The zip carries EchoXR\Hands\version.txt.

common/ holds copies of two EchoXR files the bridge and settings window
use: echoxr_common.h (plugin and loader setup) and ui.h (the UI kit).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>