v0.1.2

Reject config/write (read-only source); bump protocol deps to v0.1.21

The YAML config source is read-only — .animus/workflows.yaml and
.animus/workflows/*.yaml are the hand-edit surface. It does NOT advertise
CAPABILITY_CONFIG_WRITE, so the kernel refuses config/write up front. As
defense in depth the dispatch loop answers any config/write request with a
clean METHOD_NOT_SUPPORTED (-32001) error rather than a panic or empty reply.

Also drain in-flight handler tasks on stdin EOF (and reap completed ones each
loop) so a single piped request still gets its response flushed without leaking
JoinSet handles over a daemon-long open stdin.

Bumps animus-{config,plugin}-protocol + animus-plugin-runtime to tag v0.1.21.