Add configurable admin password via environment variable

- Add ORCHARD_ADMIN_PASSWORD env var to set initial admin password
- When set, admin user created without forced password change
- Add AWS Secrets Manager support for stage/prod deployments
- Add .env file support for local docker development
- Add Helm chart auth config (adminPassword, existingSecret, secretsManager)

Environments configured:
- Local: .env file or defaults to changeme123
- Feature/dev: orchardtest123 (hardcoded in values-dev.yaml)
- Stage: AWS Secrets Manager (orchard-stage-creds)
- Prod: AWS Secrets Manager (orch-prod-creds)

backend/app/config.py

@@ -53,6 +53,9 @@ class Settings(BaseSettings):
     log_level: str = "INFO"  # DEBUG, INFO, WARNING, ERROR, CRITICAL
     log_format: str = "auto"  # "json", "standard", or "auto" (json in production)
 
+    # Initial admin user settings
+    admin_password: str = ""  # Initial admin password (if empty, uses 'changeme123')
+
     # JWT Authentication settings (optional, for external identity providers)
     jwt_enabled: bool = False  # Enable JWT token validation
     jwt_secret: str = ""  # Secret key for HS256, or leave empty for RS256 with JWKS