audit: add AUDIT_COVERAGE.md + ASCII cleanup + CT fixes
- Add comprehensive AUDIT_COVERAGE.md documenting all 46 audit modules
across 8 sections with ~1M+ total assertions
- Pure ASCII cleanup: remove all Unicode from source/cmake/script files
(box-drawing, arrows, Greek, emoji, BOM, Georgian in comments)
- CT fix: RISC-V is_zero_mask (seqz+neg inline asm)
- CT fix: ct_compare general path (snez)
- All 188 files updated for ASCII-only compliance (Section 17 rule)
- Verified: 46/46 audit PASS on X64, ARM64, RISC-V (QEMU + Mars HW)
- Verified: 24/24 CTest PASS on X64
be528aef66