fix: refined native controls and app states

[jacobcxdev]

Summary

• Replaced custom fixed-colour row buttons with native macOS controls and removed duplicate Settings toolbar access.
• Clarified authentication, installation, settings and error copy; standardised authentication sheet widths and wrapping.
• Added simulator inventory loading, error and retry states without discarding cached inventory; guarded cancelled refreshes.
• Explained empty platform details and offered catalogue refresh when metadata is missing.
• Fixed automatic-install timer reconfiguration and Rosetta preference availability; added visionOS SDK details.
• Improved icon accessibility labels, group selection, Advanced settings scrolling and acknowledgements padding.
• Prepared version 4.1.2 (50), preserving existing preferences and account storage.

Verification

• Focused red/green regressions for timer lifecycle, Rosetta policy and runtime refresh state.
• Full local shipping suite passed: 143 tests, 149 parameterised runs, zero failures or skips on macOS 27.0 with Xcode 27.2 beta.
• Localisation checker and mutation contracts passed; 58 pre-existing tracked gaps remain unchanged.
• Fork identity and CI/release workflow contracts passed.
• Independent source review completed; runtime catalogue retry finding fixed and rechecked.
• Temporary light/dark renders covered authentication screens, four Settings panes, direct rows, details, progress controls, About and acknowledgements. The rendering harness was not added to the shipping test suite.

Verification limits

• Computer Use currently times out. Live keyboard, VoiceOver, new-build window interaction and actual increased-contrast behaviour remain unverified.
• Offscreen SwiftUI List and increased-contrast fixtures did not produce usable renders and are not counted as evidence.
• Updates was not rendered offscreen because its updater initialiser starts Sparkle and accesses real preferences.
• New catalogue translations are machine-assisted, not human-reviewed. No claim of complete HIG or accessibility conformance.
• No account logout, Xcode installation, runtime deletion or permission change was performed during the audit.