docs(readme,landing): introduce the desktop app (#201)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/desktop/electron-builder.yml

@@ -26,6 +26,11 @@ mac:
   category: public.app-category.developer-tools
   # No Developer ID yet (M4): identity null skips codesign instead of failing.
   identity: null
+  # Version-less artifact names, following the CLI bundles (penguin-darwin-arm64.tar.gz):
+  # the version lives in the Release tag and SHA256SUMS.desktop, so the download page and
+  # the OSS mirror manifest can address every installer by a stable name — and GitHub's
+  # `releases/latest/download/<name>` stays a working static link across releases.
+  artifactName: penguin-desktop-darwin-${arch}.${ext}
   target:
     - target: dmg
       arch: [arm64, x64]
@@ -33,6 +38,7 @@ mac:
       arch: [arm64, x64]
 
 win:
+  artifactName: penguin-desktop-win32-${arch}.${ext}
   target:
     - target: nsis
       arch: [x64]
@@ -50,6 +56,7 @@ nsis:
 linux:
   # The scoped package name is not a valid executable file name.
   executableName: penguin-harness
+  artifactName: penguin-desktop-linux-${arch}.${ext}
   category: Development
   maintainer: Prism Shadow <zheng@prismshadow.com>
   target: