Summary

Document the database proxy layer including proxy_connector.h, proxy_config.h, and their implementation, which enables proxied database connections but has no documentation.

Parent Issue

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

Background (Why)

The proxy layer at database/proxy/ provides database connection proxying capabilities, but there is zero documentation for this feature. Users cannot discover or use this functionality without reading source code directly.

Source files:

• database/proxy/proxy_connector.h — Proxy connection establishment
• database/proxy/proxy_config.h — Proxy configuration options
• database/proxy/proxy_connector.cpp — Implementation

Scope (What)

Add documentation covering:

1. Proxy Architecture

• Purpose and use cases for database proxying
• How proxy_connector integrates with the existing connector hierarchy
• Relationship to direct database connectors (PostgreSQL, MySQL, SQLite, etc.)

2. Configuration (proxy_config.h)

• All configurable parameters (host, port, auth, TLS, timeouts)
• Configuration examples for common proxy setups
• Environment-specific configuration patterns

3. API Reference (proxy_connector.h)

• Class interface and public methods
• Connection lifecycle (create → connect → query → disconnect)
• Error handling and retry behavior
• Thread safety guarantees

4. Usage Examples

• Basic proxy setup with PostgreSQL backend
• Proxy with TLS termination
• Connection through SSH tunnel proxy
• Load-balanced proxy configuration

5. Integration with Existing Backends

• Which database backends support proxying
• Proxy-specific limitations per backend
• Performance implications of proxied connections

Acceptance Criteria

• Proxy layer architecture documented in docs/ or relevant API reference
• proxy_config.h parameters fully documented
• proxy_connector.h API fully documented
• At least 3 usage examples provided
• Integration with existing backends explained
• Performance considerations noted