Server-side RPC for paliad's remote-tmux turns. Invoked via mRiver's
~/.ssh/authorized_keys command= restriction; dispatches on the verb in
$SSH_ORIGINAL_COMMAND. Four verbs: health, bootstrap, run-turn, reset.
Per the design (§5.4), this is the single SSH entry point for paliad-prod
on mLake. The Go service in cmd/server/main.go later constructs
RemotePaliadinService with this script as the only command the
authorized_keys entry permits.
Multi-character payloads (system prompt, user message) are base64-encoded
by the caller so they never have to be quoted through ssh's argv. The
shim validates UUID turn_ids, base64 decodes inputs, and never evals
$SSH_ORIGINAL_COMMAND.
Smoke-tested on mRiver:
- empty / unknown verb → exit 2 with clear stderr
- bootstrap with bad base64 → exit 2 BEFORE creating any pane
- health → "ok" on a clean tmux session
Refs m/paliad#12
