feat(themes): Theme Store install counts, downloads & sort (#1036)

* feat(themes): install counts, downloads, popularity & sort in the Theme Store

Each registry theme now carries an install count and a last-changed date. Store
rows show them in a dedicated meta panel (author, popularity bar, total
downloads, last changed), plus a sort dropdown (most popular / newest / name),
zebra-striped rows, a numbered pager, and a note that the stats refresh daily.
Adds a shared formatRelativeTime helper (formatLastSeen now delegates to it).

* test(themes): cover sort modes, pager jump and relative-time formatting

* fix(build): gate nvidia_quirk_active to Linux

Its only caller is the Linux branch of theme_animation_risk, so on Windows and
macOS the function was dead code and tripped clippy's -D warnings.

* docs: CHANGELOG + credits for theme store download stats & sort (#1036)

CHANGELOG.md

@@ -56,13 +56,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Themes — community Theme Store
 
-**By [@Psychotoxical](https://github.com/Psychotoxical), PR [#1009](https://github.com/Psychotoxical/psysonic/pull/1009), [#1011](https://github.com/Psychotoxical/psysonic/pull/1011), [#1012](https://github.com/Psychotoxical/psysonic/pull/1012), [#1013](https://github.com/Psychotoxical/psysonic/pull/1013), [#1014](https://github.com/Psychotoxical/psysonic/pull/1014), [#1015](https://github.com/Psychotoxical/psysonic/pull/1015), [#1016](https://github.com/Psychotoxical/psysonic/pull/1016), [#1018](https://github.com/Psychotoxical/psysonic/pull/1018), [#1020](https://github.com/Psychotoxical/psysonic/pull/1020)**
+**By [@Psychotoxical](https://github.com/Psychotoxical), PR [#1009](https://github.com/Psychotoxical/psysonic/pull/1009), [#1011](https://github.com/Psychotoxical/psysonic/pull/1011), [#1012](https://github.com/Psychotoxical/psysonic/pull/1012), [#1013](https://github.com/Psychotoxical/psysonic/pull/1013), [#1014](https://github.com/Psychotoxical/psysonic/pull/1014), [#1015](https://github.com/Psychotoxical/psysonic/pull/1015), [#1016](https://github.com/Psychotoxical/psysonic/pull/1016), [#1018](https://github.com/Psychotoxical/psysonic/pull/1018), [#1020](https://github.com/Psychotoxical/psysonic/pull/1020), [#1036](https://github.com/Psychotoxical/psysonic/pull/1036)**
 
 * New **Settings → Themes** tab: pick a theme, set the day/night scheduler, and browse a built-in **Theme Store** to install, update and uninstall community themes — with search, a dark/light filter, and full-size thumbnail previews.
 * The app now bundles six core themes (Catppuccin Mocha & Latte, Kanagawa Wave, Stark HUD, and the colour-blind-safe Vision Dark / Vision Navy); every other palette installs on demand from the [psysonic-themes](https://github.com/Psysonic/psysonic-themes) repo. Installed themes are saved locally and apply instantly at startup, even offline.
 * **Import a theme from a local `.zip`** (manifest.json + theme.css): the package is validated, you confirm its name and author, then it installs like any other community theme.
 * Themes are **free-form** — beyond recolouring, they can add their own styling and animations and react to playback / fullscreen / sidebar / lyrics state. A safety floor (no network, no scripts) is always enforced; store themes are reviewed, and imported themes install at your own risk.
 * The store paginates large catalogues, and refreshing the list no longer jumps back to the top.
+* Each store theme shows its **total downloads** and a **last-changed** date, and can be sorted by most popular, newest or name; the catalogue now has numbered page navigation. These stats refresh once a day.
 * Upgrading from an older build: an active or scheduled theme that has moved to the store and isn't installed falls back to Mocha (dark) / Latte (light).