fix(api): resolve Docker startup failures (secrets, Redis, Prisma)

- Pass BETTER_AUTH_SECRET through all 6 docker-compose files to API container
- Fix BullModule to parse VALKEY_URL instead of VALKEY_HOST/VALKEY_PORT,
  matching all other Redis consumers in the codebase
- Migrate Prisma encryption from removed $use() middleware to $extends()
  client extensions (Prisma 6.x compatibility), keeping extends PrismaClient
  pattern with only account and llmProviderInstance getters overridden

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

docker/docker-compose.build.yml

@@ -380,6 +380,8 @@ services:
       # JWT
       JWT_SECRET: ${JWT_SECRET:-change-this-to-a-random-secret}
       JWT_EXPIRATION: ${JWT_EXPIRATION:-24h}
+      # Better Auth
+      BETTER_AUTH_SECRET: ${BETTER_AUTH_SECRET}
       # Ollama (optional)
       OLLAMA_ENDPOINT: ${OLLAMA_ENDPOINT:-http://ollama:11434}
       # OpenBao (optional)