Trim Electron locale resources

[FernandoAbishai]

Summary

• keep only English and Spanish Electron/Chromium locale resources on macOS (en, en_GB, es, es_419)
• add an exact packaged locale checker used by both ad-hoc candidate and future signed release paths
• statically pin the locale allowlist and both release gates in the release workflow contract

Size

Compared with the validated PR #83 release candidate:

• app: 844,664,204 -> 798,420,936 bytes (-46,243,268 / -5.475%)
• DMG: 284,802,926 -> 273,245,955 bytes (-11,556,971 / -4.058%)

Validation

• electron-builder 26.15.3 config inheritance verified for self-contained/candidate/signed paths
• old all-locale candidate correctly fails the new checker
• rebuilt package retains exactly en/en_GB/es/es_419 in both app and Electron Framework resource roots
• packaged backend, renderer transport, creator qualification and MPS compatibility passed
• npm run release:rc:arm64 -- --require-mps passed all candidate gates from commit 229e66f
• independent read-only review: no MUST-FIX

No Developer ID signing or notarization is claimed; candidate remains ad-hoc.

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