Document Revision 1 direct-drive CAD baseline

[bostromdev]

Summary

• replace the obsolete bearing/coupler Fusion architecture with the open Revision-1 direct-drive prototype
• record the latest NEMA-17, ZX-052 V2.0, and AD8317 mechanical evidence
• define the 220 × 220 mm layout study, reversible electronics retention, direct-SMA detector/AUT carriage, and managed moving harness
• shorten and clean the Autodesk Fusion handoff
• extend repository validation to enforce the direct-drive hardware contract and inspect tracked repository artifacts only

Validation

• repository checks passed
• hardware profile validation passed
• Python: 25 passed, 2 skipped
• host firmware: build succeeded; 4/4 tests passed
• git diff --check passed

Notes

Direct drive is selected for Revision 1 but remains subject to low-acceleration prototype validation. This PR does not change GPIO assignments or firmware behavior.