feat(platform): add P1 operational maturity modules — sessions, maintenance, exports, IP rules
- modules/sessions: device session tracking, revoke one/all, admin force-revoke (9 tests)
- modules/maintenance: 4 modes (off/read_only/maintenance/emergency), bypass roles/IPs, scheduled windows (14 tests)
- modules/exports: GDPR data export jobs for users/audit/telemetry/usage/subscriptions/licenses (10 tests)
- modules/ip-rules: IP allow/deny with CIDR matching, temporary blocks with expiry (10 tests)
- cosmos-init: 4 new containers (sessions, ip_rules, export_jobs, maintenance_windows)
- 1029 platform-service tests passing across 74 test files
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