feat(vba-studio): VBA-inspired macros for office apps

Closes #25

Summary

Adds VBA Studio (src/vba-studio/) — an original VBA-inspired interpreter and in-browser worksheet host so office macros are no longer entirely out of scope.

Scope (v0)

• Sub / Dim / For/Next / If/Then/Else / MsgBox
• Range("A1").Value host API
• Comparison table in README (DOCUMENTED vs Microsoft VBA)

Tests

cd src/vba-studio && npm test — 6 passed; npm run build OK

Not Microsoft VBA; no Office binaries.