Descriptions are always English even when a translation is available on the system

Running the installer with a non-English locale, the **Description** column stays
in English, in both the *Popular Applications* and the *Repository* tab. This
happens even for applications that are fully translated and whose translated
description is already present on the machine.

Example with `LANG=ru_RU.UTF-8` and `elisa`:

* what the installer shows — `A simple music player aiming to provide a nice experience for its users`
* what is on disk, in `/usr/share/swcatalog/xml/extra.xml.gz`:

```xml
Play local music and listen to online radio
Воспроизведение хранящейся локально музыки и прослушивание интернет-радиостанций
```

KDE Discover, on the same machine, shows the Russian one.

#### Where the string comes from

The description is read from the pacman database. `MainWindow::processFile()`
takes it from the ALPM package view:

https://github.com/cachyos/packageinstaller/blob/0c33b27/src/mainwindow.cpp#L459-L461

```cpp
if (auto pkg = m_alpm_manager->get_package_view(names[0])) {
description = QString(pkg->desc.data());
}
```

which is `pkg.desc()` from libalpm (`backend-rustlib/src/pacman_cache.rs:34`), and
`PacmanCache::refresh_list()` fills the repository tab from the same field. So the
string is `pkgdesc` from the package database.

This is not something a translation can fix: `pkgdesc` is a single string per
package in `PKGBUILD`, with no language variants, so there is nowhere for a
translated version to live. `grep -ri appstream` over the repository only matches
`flatpak update --appstream`; the AppStream catalogue is never read.

Worth noting the two texts are independent, not a translation of one another —
AppStream says *"Play local music and listen to online radio"*, `pkgdesc` says
*"A simple music player aiming to provide a nice experience for its users"*.

#### The data is already there

`archlinux-appstream-data` installs `/usr/share/swcatalog/xml/{core,extra,multilib}.xml.gz`,
where each component carries a `` (the pacman package name) together with a
`` for every language it has been translated into. libappstream
picks the right language from the current locale by itself. On this machine
`appstreamcli status` reports 5633 components.

It covers packages that are **not** installed, which is the case that matters here —
`lollypop`, `ardour`, `kwave` are all absent from this system and all resolve to a
Russian summary.

Measured against the 147 packages currently in `pkglist.yaml`:

| | |
|---|---|
| in `pkglist.yaml` | 147 |
| present in the AppStream catalogue | 112 |
| **have a Russian summary available today** | **52** |

A few of them:

| package | shown now (`pkgdesc`) | available (`ru` summary) |
|---|---|---|
| `elisa` | A simple music player aiming to provide a nice experience for its users | Воспроизведение хранящейся локально музыки и прослушивание интернет-радиостанций |
| `lollypop` | Music player for GNOME | Воспроизведение и упорядочивание вашей фонотеки |
| `ardour` | Professional-grade digital audio workstation | Цифровая звуковая рабочая станция |
| `kwave` | A sound editor | Аудиоредактор |
| `kdevelop` | C++ IDE using KDE technologies | Интегрированная среда разработки с широкими функциональными возможностями и поддержкой расширений для C/C++ и других языков программирования |

Russian is only the language I can check; the same catalogue carries the other
languages the installer is already translated into.

#### Side effect: search does not work in the user's language

`findPopular()` matches against the Description column, so with English-only
descriptions a Russian user typing `музык` ("music") gets no results at all,
even though `elisa` is right there in the list.

#### How other package front-ends handle it

* **pamac** loads `/usr/share/swcatalog/xml/.xml.gz` through `AppStream.Metadata`
(`libpamac/src/appstream_plugin.vala:178-182`), builds a `pkgname_apps_cache`
hash table (same file, line 150), and falls back to `alpm_pkg.desc` whenever the
AppStream summary is missing (`libpamac/src/alpm_package.vala:148-164`).
* **KDE Discover** builds a `packageToApp` hash the same way
(`libdiscover/backends/PackageKitBackend/PackageKitBackend.cpp:407`) and also uses
`componentsByBundleId(AppStream::Bundle::KindPackage, pkg_name, false)`
(same file, line 590).
* **GNOME Software** queries its libxmlb silo with
`components/component[@type='desktop-application']/pkgname[text()='%s']/..`
(`plugins/core/gs-plugin-appstream.c:1025`).

All three keep the `pkgdesc` as a fallback. None of them set the locale explicitly —
libappstream derives it from the environment.

#### Suggestion

Read the summary from the AppStream catalogue and keep `pkgdesc` as the fallback.
`AppStreamQt` is Qt6 and integrates into the existing CMake setup as an optional
dependency, so builds without it would behave exactly as today.

I have this working locally against `develop` — roughly 60 lines across
`CMakeLists.txt`, `mainwindow.hpp` and `mainwindow.cpp`. It builds and runs, both
tabs show translated descriptions, and Russian search works. Cost is one pass over
the OS catalogue at start-up, measured at about 75 ms.

Happy to open a PR if that is a direction you would consider.

### Related

This is a concrete answer to #12 ("description and package information display should be changed"), which has been open without details since 2024.

Start with MainWindow::processFile() in src/mainwindow.cpp, findPopular(), PacmanCache::refresh_list(), and the dependency setup in CMakeLists.txt; the related declarations are in mainwindow.hpp. Review how pkg.desc() currently supplies descriptions, then verify that both tabs use the locale-aware catalogue when available, fall back to pkgdesc when it is not, and allow searches such as Russian “музык”.

Written by the indexing model from the issue text.