Summary

Document the storage backend system including all 8 supported backends, selection criteria, data retention policies, and custom backend implementation guide.

Parent Issue

Part of: [EPIC] docs: Address documentation gaps across all ecosystem systems (kcenon/common_system#325)

Background (Why)

monitoring_system supports 8 storage backends (Memory, File, SQLite, PostgreSQL, MySQL, S3, GCS, Azure) via storage/storage_backends.h, but there is no documentation explaining when to use each backend, how to configure them, or how to implement custom backends.

Source files:

• include/kcenon/monitoring/storage/storage_backends.h — All backend implementations

Scope (What)

Create docs/guides/STORAGE_BACKENDS.md covering:

1. Storage Architecture

• Backend abstraction interface
• Data model (metrics, traces, alerts)
• Read/write patterns
• Retention and cleanup

2. Backend Comparison

3. Configuration per Backend

• Connection strings and authentication
• Buffer sizes and flush intervals
• Retention policies
• Cleanup strategies

4. Custom Backend Implementation

• Backend interface contract
• Required methods
• Error handling requirements
• Testing approach

Acceptance Criteria

• All 8 backends documented with configuration
• Comparison table with selection criteria
• Retention and cleanup policies documented
• Custom backend implementation guide