desktop: add Russian translations

[wehrwolfmann]

Same thing I just sent for the Kernel Manager: the launcher entry is what a user sees before the program starts, and on a Russian desktop it is the only English line in that part of the menu — "SchedExt GUI Manager / Manage scx schedulers" — even though the app has a Russian catalogue in lang/.

This adds Name[ru], GenericName[ru], Comment[ru] and Keywords[ru] next to the Japanese lines, in the same style. SchedExt and SCX stay in Latin as names; only the descriptive words are translated, and "планировщик" matches what scx-manager_ru.ts already uses for scheduler.

The Keywords[ru] line repeats the original cachyos;system;kernel; before the Russian words on purpose: a translated Keywords line replaces the untranslated one instead of extending it, so without that a Russian session would stop finding the app by "kernel". The Japanese line handles it the same way.

desktop-file-validate is clean.

[vnepogodin]

need rebase

[wehrwolfmann]

@vnepogodin sorry for the silence — you asked for a rebase on 6 Sep, I pushed it the same day and then never came back to say so.

Where it stands now: the branch is rebased straight onto master (121bae0), one commit, no conflicts, GitHub marks it mergeable.

One detail that may not be visible from your side: the Build and Checks runs from that rebase are still sitting in "waiting for approval" and never started a single job, so the PR shows no green checks for reasons that have nothing to do with the change itself. The earlier pair from 17 Aug sat there until GitHub's 30-day limit and then turned into "Run failed — No jobs were run" mails last night. They need the approve-and-run click before they can say anything.

Nothing else outstanding from my side.