fix: sanitize tauri signing key for gui release

[TrueNine]

Summary

• strip UTF-8 BOM from the Tauri signing key before GUI builds consume it
• route all GUI build and debug workflows through the same key normalization path
• bump workspace versions to 2026.10314.10703 after the partially published 2026.10314.10606 run

Validation

• pnpm exec tsx .githooks/sync-versions.ts 2026.10314.10703
• workflow static contract check
• prior local build/test suite from the 2026.10314.10606 release prep remained green