After autospawn spawns zot, the agent was never registered in the
local SQLite store. The scheduler only routes tasks to registered
agents — so every task stayed stuck in 'queued' forever.
This commit adds a store.register_agent() call right after the spawn
succeeds, before the bootstrap RPC prompt. The agent is registered
with [shell, freebsd, code] capabilities and the current hostname.
Uses try_lock() to avoid blocking the daemon on store contention.
