Third slice of Issues + Systems (spec #825).
routes/systems.py (nested /api/projects/<id>/...): GET/POST systems (list adds
per-system open_issue_count via one grouped query), GET/PATCH/DELETE a system
(GET returns records split into issues/tasks/notes), GET .../systems/<id>/records
(kind/open_only filters), GET .../issues (project's open issues for the project
view + dashboard roll-up). login_required; project access via get_project_for_user;
writes gated by can_write_project (clean 403); system.project_id verified to match
the path. Blueprint registered in app.py.
services/systems.py: + open_issue_counts_by_system (one grouped query) and
list_issues (project issues, open by default).
Tests: structural (blueprint registered + in app, handlers callable, service
contracts take user_id) — matches the house route-test pattern.
Refs plan 825 (S3).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
