MacPad 1.0.3

Adds keyboard/window polish and release QA documentation.\n\nChanges:\n- Cmd+Shift+N explicitly opens a new window.\n- Cmd+W closes the current tab/window through the normal unsaved-change prompt.\n- Window menu includes previous/next tab commands.\n- README now includes release/license/macOS badges and links to QA.md.\n- App version bumped to 1.0.3 build 4.\n\nSHA-256: 7002404359b0ff92d0fec06f3453cbcfd7d9ea1305e682a9ef9e8c3c7e6e2b8a