Without this, app.quit() destroys windows instantly, creating a jarring
pop-out. Now all windows fade out over 250ms (matching the fade-in)
before the app exits. Uses the same CSS opacity transition — just
removes the "visible" class and defers quit via glib timeout.
First launch with blur blurs and saves to ~/.cache/moonset/. Subsequent
starts load the cached PNG directly (~9x faster). Cache invalidates
when wallpaper path, size, mtime, or sigma changes.
Feature-parity with Python v0.2.0. Same CSS, same UI, same actions.
Single 3.1 MB binary with embedded resources (CSS, wallpaper, avatar).
Modules: power.rs, i18n.rs, config.rs, users.rs, panel.rs, main.rs
45 unit tests passing. Python sources retained as reference.
