#1043 Add database query performance logging for slow queries

[vic-Gray]

Area: backend · Effort: S

What: Log all database queries exceeding 100ms with their SQL, parameters, and execution time, and expose a summary of the slowest queries.

Why: Slow queries are the most common performance bottleneck in web applications and are invisible without query logging. Early identification prevents them from becoming production incidents.

Acceptance Criteria:

• Queries > 100ms are logged at WARN level with full SQL
• Queries > 1000ms are logged at ERROR level and emit a metric
• A GET /admin/slow-queries endpoint returns the top 10 slowest query types from the last 24 hours
• The slow query threshold is configurable via env var

Hints:

• Use TypeORM's logger option with logSlowQueries: true and a custom logger class
• backend/src/database/slow-query-logger.ts
• Aggregate slow query data in Redis with a 24-hour TTL