chore(platform-service): wire P2+P3 modules into server + cosmos-init
- server.ts: register cdnRoutes, searchRoutes, dunningRoutes (P2)
- server.ts: register tenantRoutes, retentionRoutes, backupRoutes, apiVersioningRoutes (P3)
- cosmos-init.ts: 17 new containers across 7 modules:
CDN: cdn_assets, cdn_purge_requests, cdn_origin_configs
Search: search_index, search_suggestions
Dunning: dunning_campaigns, dunning_policies
Tenants: tenants, tenant_members, tenant_invites
Retention: retention_policies, retention_jobs
Backups: backups, restores, backup_configs
API Versioning: api_versions, api_version_pins
- Total platform-service modules: ~41, tests: 1239
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