Convert TouchEngine SDK to git submodule (v3.3)

[keithlostracco]

Summary

• TouchEngine SDK: Replaced committed SDK files with a git submodule pinned to tag 3.3 (was v3.0)
• source/comp.cpp: Updated TEInstanceConfigure call — SDK 3.3 removed the UI mode parameter (TEUIWindows/TEUINone), now takes 3 args instead of 4
• CI workflows: Added submodules: true to all actions/checkout steps (ci.yml, wheels.yml, docs.yml)
• README.md: Added --recurse-submodules clone instructions and git submodule update --init fallback
• .gitignore: Removed vendored SDK bypass rules (no longer needed)

SDK 3.0 → 3.3 changes

• 3.2: Added TEInstanceSetPreferredEnginePath() / TEInstanceGetConfiguredEnginePath(), GPU selection fixes
• 3.3: Added TEInstanceLinkGetChoices(), fixed texture transfer and duplicated callback issues

No other breaking API changes — all additive.

Test plan

• Build succeeds against SDK 3.3
• 01_load_comp_basic.py works
• 06_tops.py works (internal time)
• 10_external_time.py works (external time, both modes)
• Tested with latest TouchDesigner build