The visibility state of the inspector panel should be remembered separately per preview handler.

Examples:

• Hex preview should remember its own last inspector visibility state.
• SQLite preview should remember its own last inspector visibility state independently.
• The design should also accommodate other preview handlers that may gain an inspector panel later.

This should preserve the user's choice across preview reloads and application restarts.

Starting implementation on a dedicated branch from develop. First step is persisting inspector visibility per preview context, followed by the new general shutdown setting.

Step 1 implemented locally on the shared working branch: inspector visibility is now persisted immediately per preview context via shared settings. The main hex preview and the SQLite cell viewer each remember their own last inspector visibility state across reloads and restarts. Builds succeeded for ZPreview, ZPreview.SQLitePreview, and ZPreview.Tests.

Implemented on branch t-b9eec11f34-911ac8c349-preview-settings in feccbc2177. Inspector visibility is now persisted immediately per preview context, so the main hex preview and the SQLite cell viewer remember their own last inspector visibility state across reloads and restarts. I built ZPreview, ZPreview.SQLitePreview, and ZPreview.Tests, but I could not run the WinForms runtime behavior on this Linux host because Microsoft.WindowsDesktop.App is unavailable, so leaving this in Review for Windows-side verification.