Feature: Add experiments domain

[Brad-Edwards]

Description

Add a new experiments domain to support tracking scientific experiments through their full lifecycle.

Scope

• Create Experiment entity with lifecycle states: PLANNED → DESIGNED → IN_PROGRESS → COMPLETED → ANALYZED
• Implement state transition validation (experiments can only move forward through the lifecycle)
• Fields: title, description, hypothesis, methodology, results, conclusions, status, dates
• Link experiments to papers and research notes via ResearchLink
• Create repository, service, and API controller layers
• Add domain events for state transitions

Acceptance Criteria

• Experiment entity with all lifecycle states
• Valid state transitions enforced (PLANNED → DESIGNED → IN_PROGRESS → COMPLETED → ANALYZED)
• Invalid state transitions rejected with appropriate errors
• Full CRUD API endpoints for experiments
• Experiments can be linked to papers and notes
• Unit tests for state transitions and business logic