fix(appearance): sync UI state with theme config on import and reset

[istekhar8966]

This PR is a clean version of the fix previously submitted in #1904. It addresses the issue where the UI selection state (Roundness and Density) was not syncing with the applied theme during Import or Reset.

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[garrettjwilke]

setting a theme to:

• light
• square
• compact

export -> change some things around -> import

it correctly sets the light mode, and sets the square style, but the density is not correctly set. it shows in the UI that Comfortable is set, but the actual setting is set to Compact.

this works, with one small exception which is the Interface Density is incorrectly set after importing.

[leviport]

Everything is syncing as expected when importing and resetting.

Regression testing passed:

Checklist

Network & Wireless

Wi-Fi

• Able to disconnect from and connect to a network.

Desktop

Wallpaper

• Clicking a different wallpaper switches to it immediately
• Leaving the page and coming back does not change the wallpaper

Appearance

• Open a COSMIC app and a GNOME app. When switching between Dark and Light mode, the COSMIC app switches immediately, and the GNOME app switches after restarting.
• Changing the accent color works.
• Changing the roundness style works and does not affect other aspects of the theme (e.g. color mode).
• Changing the interface density works.

Panel

• Enable tiling. "Automatically hide panel" takes effect immediately.
• Disable tiling; maximize a window. "Automatically hide panel" takes effect immediately.

Dock

• Enable tiling. "Automatically hide dock" takes effect immediately.
• Disable tiling; maximize a window. "Autommatically hide dock" takes effect immediately.
• Changing position on screen works.
• All Style settings take effect as expected.

Displays

• Plug in a second display. Displays can be rearranged via dragging.

Sound

TBD after devices/profiles are fixed.

Power & Battery

• Changing power mode takes effect and is reflected by top panel applet.

Input Devices

Touchpad

• All click behavior settings work as expected.
• All scrolling settings work as expected.

Applications

Default Applications

• Changing the default terminal affects Super-T shortcut.

X11 Applications Compatibility

• Global Shortcuts in X11 Applications works (in e.g. Discord).

Time & Language

Date & Time

• Changing time zome works.
• Toggling 24-hour time takes effect in Settings preview, on top panel, and on the lock screen.
• Toggling seconds takes effect in Settings preview and on top panel.
• Changing first day of week takes effect in Calendar applet.
• Turning date on/off for applet works.

System & Accounts

About

• Changing hostname works (check terminal prompt).