feat(operator): visual-only screens with real-data overview (O.7)

- Overview (pages/index.vue): KPIs from real /tenants /partners /users,
  status meter, recent + needs-follow-up tables. Mock activity stream and
  incident banner overlay come from data/fixtures.ts.
- Operator team: real GET /users filtered to platformAdmin === true,
  with last-seen + tenant counts.
- Users (global): real read with All/Admins/Inactive views and search.
- Infrastructure / Feature flags / Audit: mock fixtures only — wiring to
  real backends (Prometheus, OpenFeature, append-only audit) is tracked
  as follow-ups in OPERATOR-PLAN.md.
- Placeholder pages (support/billing/reports/settings) via OpPlaceholder.
- Shared: Stat, MetricCell, OpPlaceholder components, /api/users proxy,
  PlatformUser type.
- .gitignore: scope the docker volumes data/ rule so apps/*/data/ is
  tracked again (operator carries mock fixtures there).

.gitignore

@@ -29,8 +29,11 @@ logs/
 *.swo
 .DS_Store
 
-# Docker volumes data (when bind-mounted)
+# Docker volumes data (when bind-mounted) at the infra layer
 data/
+# But keep app-level data/ dirs — operator carries mock fixtures there.
+!apps/*/data/
+!apps/*/data/**
 
 # Coverage
 coverage/