…zed modules + other refactoring

Refactor the admin usage analytics system by breaking down the 2900-line
monolithic AdminUsageStatsService into focused, single-responsibility
services following established architectural patterns.

Architecture improvements:
- Extract aggregation logic into AdminUsageAggregationService (2078 lines)
- Extract trend calculation into AdminUsageTrendCalculator (472 lines)
- Extract data enrichment into AdminUsageEnrichmentService (344 lines)
- Extract export functionality into AdminUsageExportService (253 lines)
- Extract shared utilities into admin-usage.utils.ts (412 lines)
- Reduce main orchestrator to coordinating extracted services

New infrastructure utilities:
- Add advisory-lock.utils.ts for PostgreSQL advisory locks
- Add date-validation.ts for date range validation
- Add pagination.utils.ts for consistent pagination handling
- Add admin-analytics.config.ts for centralized configuration
- Add rate-limit.config.ts for API rate limiting

Frontend enhancements:
- Implement reusable usePagination hook
- Add ModelBreakdownTable and UserBreakdownTable components
- Enhance chart components with improved accessibility
- Update i18n translations across 9 languages

Testing & documentation:
- Add 39 new test files for comprehensive coverage
- Add 72 new documentation files including:
  - Detailed refactoring session logs (phases 0-6)
  - Code review checklist and concurrency strategy
  - Error handling guide and pattern reference updates
- Reorganize docs into archive/ structure

Configuration:
- Add configurable cache TTL via ConfigContext
- Implement environment-based admin analytics settings
- Add rate limiting configuration options

Database improvements:
- Add test database isolation helpers
- Implement advisory locks for race condition prevention
- Add migration rollback utilities

Benefits:
- Improved maintainability through separation of concerns
- Better testability with focused service modules
- Enhanced code reusability across features
- Clearer boundaries between business logic layers
- Comprehensive documentation of refactoring process

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Signed-off-by: Guillaume Moutier <guimou@users.noreply.github.com>
Co-authored-by: Claude