core: implement audit log for all admin operations

[EmeditWeb]

Problem

Admin operations leave no audit trail. If something
goes wrong there is no record of who did what.

What To Build

1. Create audit_logs table in Supabase
2. Create AuditService and AuditInterceptor
3. GET /admin/audit-logs endpoint
4. Immutable INSERT-only design

Files To Touch

• src/audit/ (new module)
• src/common/interceptors/audit.interceptor.ts
• All admin controllers
• supabase/migrations/[ts]_audit_logs.sql

Acceptance Criteria

• All admin actions logged
• Before and after state captured
• Logs immutable (no updates allowed)
• Searchable via endpoint
• npm run build passes

Mandatory Checks Before PR

• npm run build passes
• No any types
• PR references this issue