agentbridge: Mise channel via UBI backend

[espetro]

Context

Mise is a 5th distribution channel. UBI backend works day one with one line in mise.toml:

[tools]
agentbridge = "ubi:espetro/agentbridge"

UBI downloads the GitHub Release binary, places it in ~/.local/share/mise/installs/agentbridge/, symlinks to shims. Zero extra infra.

Tasks

• Add a mise.toml example to README showing the one-liner
• Document UBI in the README install matrix
• Verify agentbridge --version works after mise install
• (Post v0.2.0) Create espetro/mise-agentbridge core plugin for full UX: mise use agentbridge@0.2.0, mise ls-remote agentbridge, version listing
• (Post v1.0.0) Submit to upstream jdx/mise registry for zero-config install

Source

• README.md (modify)
• New repo: espetro/mise-agentbridge (post v0.2.0)
• Plan: .agents/plans/2026-06-14-v0.2.0-distribution-pivot.md