v2.19.0

What's Changed

• Define the MUCP Message contract under proto/mucp by @asim in #2158
• Reduce idle inbox and agent status polling by @asim in #2160
• License protocol contracts under Apache-2.0 and clarify commercial terms by @asim in #2159
• Point commercial enquiries to Micro GitHub Sponsors by @asim in #2161
• Add standalone mu-cli client over MUCP by @asim in #2162
• Complete desktop menus, window restore and sign-in feedback by @asim in #2163
• Fix blog tag separators and updated-date spacing by @asim in #2164
• Separate MUCP specification and test independent agent interoperability by @asim in #2165

Full Changelog: v2.18.1...v2.19.0