[deploy-plugin DPB-4] Host-owned deploy shell split + router rewired over core contracts

[rickylabs]

Part of #892 (RFC #891; corpus .llm/runs/plan-deploy-plugin--seed/ r5).

Split the deploy group into a host-owned shell (owns desktop, shared help, the future install hint) with the target router rewired over the core contracts; fix the stale "Windows Service" group description. Anti-scope: zero verb changes; the desktop subgroup is not moved (DP-6 M-16/R-M4).

Acceptance

• gate: help-output goldens unchanged except the description fix
• gate: desktop verbs untouched by the diff
• gate: e2e:cli green

Metadata

Dependencies: DPB-1, DPB-3
Delivery shape: thin-router refactor