feat(mise): add herdr, the agent multiplexer

[natevick]

cmux is macOS-only, so an Omarchy move leaves us without it. herdr is the closest replacement: one Rust binary (no Electron), a background server whose panes survive detach and network loss, per-pane working / blocked / idle state, and a socket API agents can drive. herdr --remote <host> is a thin SSH client, which is already how the agent box gets used.

Pinned to 0.8.2 rather than latest — it's pre-1.0 (220 open issues) and ships about weekly. This would be the runtime agent sessions live in; an unattended bump mid-week isn't worth the convenience. Same reasoning as the zig pin above it.

mise resolves it through the aqua backend to a prebuilt binary, so the npm-backend lifecycle-script problem (aube) doesn't apply.

Verified on the agent box

$ mise use -g herdr@0.8.2
mise herdr@0.8.2 ✓ installed
$ herdr pane list
{"panes":[{"pane_id":"w1:p1","agent_status":"unknown",...}]}
$ herdr pane run w1:p1 bash -lc 'uname -sm'
$ herdr pane read w1:p1
Linux x86_64
$ herdr server stop        # nothing left running

Template renders and parses:

$ chezmoi execute-template < .../cli-tools.toml.tmpl | python3 -c 'tomllib…'
OK — herdr pin: 0.8.2

The parse check was sabotaged (unterminated string) to confirm it can actually fail — TOMLDecodeError, as expected.

Not in this PR

Nothing is switched over. cmux stays as-is; this only makes herdr available so it can be lived in before any decision.

🤖 Generated with Claude Code

https://claude.ai/code/session_015TTYfJBxmRZLfz73ZQyzyZ