fix(compiler): retain exact opaque field labels

[abrichr]

Summary

• retain one exact, row-aligned field label for opaque select controls
• require exact OCR uniqueness while preserving legacy fuzzy landmark serialization
• revalidate the same selected field after focus before any option input

Safety contract

• duplicate exact labels refuse instead of selecting the first candidate
• low-confidence duplicate OCR still contributes to ambiguity
• a moved post-focus target halts before bulk type or Enter
• legacy sealed bundle digests remain unchanged

Validation

• 216 affected tests passed
• full package mypy and strict safety mypy passed
• Ruff and diff checks passed
• independent review found no high or medium issue
• public changes contain only generic mechanisms and synthetic geometry

The retained private OpenEMR recording now compiles its first opaque select with the exact independent field label, without publishing application data or tuning.