[codex] add macOS alpha build path

[salim4n]

Closes #54

What changed

• Made the Studio desktop build produce an unsigned macOS .app alpha bundle via tauri build --bundles app --ci --no-sign.
• Updated Tauri alpha metadata: product/window name, app-only bundle target, publisher, category and descriptions.
• Documented the local build command, artifact path, metadata and signing/notarization/DMG gaps.
• Removed an unused Rust variable surfaced by the desktop build.

Validation

• bun run build:studio:desktop
• bun run ci