feat: add AMD GPU tools, media packages, and productivity module

Task 3 - Gaming profile:
- Add gpu.nix with ROCm runtime/smi/info and vulkan-tools
- Import gpu.nix in gaming profile aggregator

Task 4 - Media profile:
- Add unimatrix to yt-dlp.nix packages
- (plexamp, webcord, mpv config were already present)

Task 5 - Desktop apps:
- Add productivity.nix with pomodoro-timer
- Import productivity.nix in desktop apps aggregator

home/desktop/apps/default.nix

@@ -1,9 +1,10 @@
-# Desktop apps aggregator — Obsidian, Office, web apps, and crypto tools.
+# Desktop apps aggregator — Obsidian, Office, web apps, crypto tools, and productivity.
 {...}: {
   imports = [
     ./obsidian.nix
     ./office.nix
     ./webapps.nix
     ./crypto.nix
+    ./productivity.nix
   ];
 }