runtime: vm agents get zooid_* context tools via --mount-socket #136

runtime: vm agents have no zooid_* context tools. ZOD109 cycle 1 turned them off because the per-agent context socket couldn't reach the guest. The daemon logs socket=(unavailable: runtime vm has no host socket …), and the zooid-tasks pi extension isn't installed for vm agents.

ZOD128 (#131) added --mount-socket for the credential proxy. That proxy's host Unix socket reaches the guest at /run/zooid/model.sock, and the ZOD128 smoke run used it end to end. The per-agent context socket can be mounted into the guest the same way.

Work:

• Mount the agent's context socket into the guest and point ZOOID_DAEMON_SOCK at the guest path. Today build-registry.ts sets it only for container runtimes.
• Get the context-mcp binary into the guest. smolvm still takes no file mounts, so it has to come from the image, a directory mount, or guest setup.
• Lift the cycle-1 gates: contextUnavailableAgents, and the zooid-tasks extension skip for vm agents.

This probably makes the TCP context listener that ZOD109 planned for a later cycle unnecessary.

Found while running the ZOD128 smoke test (#131). This will be a plan-only cycle of ZOD109.