Send the build's git describe as the GMCP client version

[ctoth]

What

Core.Hello sent version: '0.1' for every build. It now sends the build's git describe string, the same value Preferences shows (for example v0.7.0-670-g9d2d9f5a).

Why

The MOO's new @issue command attaches the reporter's client name and version to each report. With a fixed 0.1, a client bug report could not say which build it came from.

Checked

• The MOO stores this value in $gmcp.client_info and returns it from $client_utils:client_version. Nothing there parses it as a number (searched the 2026-10-06 04:22 UTC database dump for client_version and client_info). The client name is unchanged, so using_official_client still matches.
• npx vitest run src/gmcp/session.test.ts: 7 passed. The startup test now asserts the hello carries the commit string and that the string is not empty.
• npm run typecheck and biome lint on the two files: clean.

Not checked

• A live login with this build, and @issue showing the new version. That needs a deploy.