Rename app to Oikos (was oikos-desktop)

- Binary: oikos-desktop → Oikos
- Bundle: oikos-desktop.app → Oikos.app
- Install path: /Applications/Oikos.app
- Auto-update paths updated
- CI Linux binary renamed

cmd/desktop/Taskfile.yml

@@ -4,7 +4,7 @@ tasks:
   build:
     summary: Build the Oikos desktop app
     cmds:
-      - go build -o build/bin/oikos-desktop .
+      - go build -o build/bin/Oikos .
     env:
       CGO_ENABLED: 1