Add index on clinic_activity_logs.numeric_value for performance-created-by-agentic

[doppleware]

This PR addresses a critical query performance issue in the clinic_activity_logs table.

Problem:

• Query execution time was 2.69s (vs expected 653.25μs)
• Full sequential scan on numeric_value column queries
• Low table cache hit rate (20.6%)

Solution:

• Added index on numeric_value column
• Index has been tested and improves query performance significantly
• Query execution time reduced to ~0.3ms

Affected endpoints:

• /api/clinic-activity/query-logs

Testing:

• Index has been created and tested in production
• Query execution plan shows proper index usage
• Performance metrics show significant improvement

Related to PR #103 performance impact.