Closes the REST gap S4b's UI needs (S2 only extended MCP tools):
- routes/tasks.py: create/update accept system_ids (set-semantics) + arose_from_id;
GET/create/update return the task's associated systems. kind=issue already
flowed via task_kind. Associations set via services/systems (ACL-checked;
can_write_note already gated).
- services/dashboard.py: _open_issues section (owner-scoped, ranked like other
task lists, capped) added to build_dashboard. Dashboard test updated for the
new key.
Refs plan 825 (S4b, backend half).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
bvandeusen
79040fe5db