feat: initialize rust backend with axum server, seaorm models, and project scaffolding

PROJECT_MGMT/coding_standards.md

@@ -89,12 +89,17 @@ paths:
   database: "./data/zhealth.db"
   logs: "./logs"
 
+logging:
+  level: "info"  # trace | debug | info | warn | error
+
 auth:
-  jwt_secret: "${JWT_SECRET}"  # Loaded from env
-  token_expiry_hours: 24
+  session_secret: "${SESSION_SECRET}"  # Loaded from env
+  session_expiry_hours: 24
+  cookie_name: "zhealth_session"
 
 ai:
   provider: "gemini"  # gemini | openai | anthropic
+  model: "gemini-3-flash-preview"
   api_key: "${AI_API_KEY}"
 ```