docs: update CONTRIBUTING, remove wails3 CLI dependency

- Makefile desktop target uses go build directly (no wails3 required)
- CI workflow simplified: go build instead of wails3 build
- CONTRIBUTING: add make install, desktop auth docs, auto-update docs
- CONTRIBUTING: add file listing for icon.png, icon.icns, Taskfile, plist

.gitea/workflows/desktop.yml

@@ -37,12 +37,8 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y libgtk-3-dev libwebkit2gtk-4.1-dev
 
-      - run: go install github.com/wailsapp/wails/v3/cmd/wails3@latest
-
-      - run: wails3 build
+      - run: CGO_ENABLED=1 go build -o build/bin/oikos-desktop .
         working-directory: cmd/desktop
-        env:
-          CGO_ENABLED: 1
 
       - run: |
           cd cmd/desktop/build/bin