fix: stale mur-mur-v2 references and intra-workspace dependency versions

The repository was renamed to murmur on 2026-08-03 but three surfaces kept the
old slug:

- README quickstart ran 'git clone .../murmur.git && cd mur-mur-v2' — the very
  first command every new user runs failed with 'no such directory'
- prep-publish.mjs stamped a dead repository URL into published package metadata
- production-file-deploy.sh defaulted to a dead clone URL

Also bumped intra-workspace deps to match the 2.5.0 versions: broker-nats and
mcp-server pinned to @murmurv2/core ^0.4.0, mcp-server to broker-nats ^0.3.0.
Without this, publishing broker-nats@0.3.0 would resolve core to the pre-signed-ACK
0.3.x line.

Removed a duplicate signed-ACK entry that landed in the README's v2.3 section;
it belongs to v2.5 and is documented there.

Build green, 213/213 tests pass.