feat: German customer-facing desktop entry and AppStream metadata

Launcher shows "PC-Heini Fernwartung" with a plain-language description of
what the program does (remote support after the user's consent) instead of
the internal "HeiniRemote Agent — connects this machine to a HeiniRemote
server". English translations via Name[en]/xml:lang. Keywords make it
findable via PC-Heini, pcheini, Fernwartung, Fernhilfe, Support, HeiniRemote.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

de.pc_heini.HeiniRemoteAgent.desktop

@@ -1,9 +1,13 @@
 [Desktop Entry]
 Type=Application
-Name=HeiniRemote Agent
-Comment=Remote maintenance agent — connects this machine to a HeiniRemote server
+Name=PC-Heini Fernwartung
+Name[en]=PC-Heini Remote Support
+GenericName=Fernwartung
+GenericName[en]=Remote Support
+Comment=Erlaubt PC-Heini, diesen Computer nach Ihrer Zustimmung aus der Ferne zu warten
+Comment[en]=Lets PC-Heini service this computer remotely, after you grant access
 Exec=heiniremote-wrapper.sh
 Icon=de.pc_heini.HeiniRemoteAgent
 Terminal=false
 Categories=Network;RemoteAccess;
-Keywords=remote;support;fernwartung;
+Keywords=PC-Heini;pcheini;pc heini;Heini;Fernwartung;Fernzugriff;Fernhilfe;Support;Hilfe;HeiniRemote;remote;