fix: use real database query in Supabase health check

[EmeditWeb]

Problem

In health.service.ts (line 66), the database health check uses supabase.auth.getSession() which checks the Supabase auth service, not raw database connectivity. A healthy auth service but dead database would pass this check, giving a false positive.

Root Cause

The health check was implemented using the convenience method rather than a direct DB query.

What To Build

1. Replace with a raw DB query: SELECT 1 from Supabase
2. Keep the auth check as a separate metric
3. Return both DB and auth health in the response

Files To Touch

• src/modules/health/health.service.ts — line 66 fix DB check

Acceptance Criteria

• DB health check uses SQL query, not auth check
• Auth check remains as separate metric
• Build passes

Mandatory Checks

• context/ files read
• npm run build passes
• PR references this issue