Fix settings back button navigation

[ManorDev]

Fixes #715

Changes

• Use replace() instead of push() when navigating between Settings pages so tabs don't accumulate in router history.
• Preserve the original route for the Settings back button.
• The Back button now returns directly to the screen from which Settings was opened.

Testing

• Manually tested navigation through multiple Settings pages.
• Verified Back returns directly to the original screen.
• cargo test -p oneclient_app — 59 passed.
• cargo clippy -p oneclient_app --all-targets — passed.
• git diff --check — passed.