P1-2: Add onRequest auth hook to reject anonymous requests on all 7
VoicePrint endpoints. Previously, the auth middleware always attached
a placeholder user (id='anonymous'), so per-route userId checks passed
for unauthenticated clients.
P1-3: Replace JSON body parsing with @fastify/multipart for POST
/endpoints (/enroll, /analyze, /batch). Fastify JSON parser cannot
produce Buffer from request.body; multipart/form-data is required
for audio file uploads. Added 50MB file size limit.
4d30bacc53