[Kotlin] Implement N+1 Query Solution with Exposed eager loading

[davideme]

Task

Implement the ?include= query parameter for eager loading in Kotlin/Exposed.

Endpoints

• GET /buildings with ?include=rooms or ?include=rooms.lamps
• GET /buildings/{id} with ?include=rooms.lamps
• GET /buildings/{id}/rooms with ?include=lamps
• GET /rooms/{id} with ?include=lamps,building

Functional Requirement

Must minimize database queries regardless of the number of entities returned.

Implementation Hints

• Use Exposed's leftJoin with manual result mapping
• Or use load() with with() for eager loading references
• Parse the include parameter and build dynamic queries

Acceptance Criteria

• ?include=rooms returns buildings with nested rooms
• ?include=rooms.lamps returns buildings with rooms and lamps
• Query count does not increase with number of buildings (verify with SQL logging)

Parent Issue

Relates to #289