fix: prisma connection exhaustion & firebase lazy init

- prisma/schema.prisma: tambah binaryTargets debian & linux-musl untuk Docker
- src/lib/prisma.ts: pakai global singleton di dev & prod, hapus eager $connect()
- src/lib/firebase-admin.ts: lazy initialization agar tidak crash saat build time
- .env.example: lengkap dengan semua env variable + connection_limit & pool_timeout

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

prisma/schema.prisma

@@ -4,7 +4,7 @@
 generator client {
   provider      = "prisma-client-js"
   engineType    = "binary"
-  binaryTargets = ["native"]
+  binaryTargets = ["native", "debian-openssl-3.0.x", "linux-musl-openssl-3.0.x"]
 }
 
 datasource db {