Closes the addressing gap that left a waiting `agenthub work` blocked: the
remaining Win tasks were titled "Win L2: …" / unassigned, so they matched
no agent and the daemon waited forever.
`agenthub task assign <id> --agent <name>` sets assignedTo WITHOUT claiming
(status stays open) and fires task/updated — so an agent's blocked `work`
re-checks, matches via assignedTo, and auto-claims it. The architect can now
route a specific open task to a specific agent and have its daemon pick it up.
- taskService.assignTask; PATCH /tasks/:id handles assignedTo-without-status;
remoteClient.assignTask; CLI `task assign`.
- test: assign keeps status open + sets assignedTo; start/work then claims it
via the assignedTo match. 122/122 green.
Bump 0.5.0 -> 0.6.0.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>