Refactor response handling and health check endpoints

- Enhance response model with additional fields and validation
- Update health and server router implementations
- Improve frontend type definitions and API integration
- Clean up documentation

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/models/response.py

@@ -94,7 +94,7 @@ Note on field naming:
 - All responses with multiple items include a "total" field.
 """
 
-from typing import Generic, TypeVar
+from typing import Generic, Literal, TypeVar
 
 from pydantic import BaseModel, ConfigDict, Field
 
@@ -326,3 +326,51 @@ class ErrorResponse(BanGuiBaseModel):
         default=None,
         description="Unique ID for correlating this error with request logs on both frontend and backend.",
     )
+
+
+class HealthResponse(BanGuiBaseModel):
+    """Standardized response for the health check endpoint.
+
+    Fields:
+        status: Application health status — 'ok' when healthy, 'unavailable' otherwise.
+        fail2ban: fail2ban daemon status — 'online' or 'offline'.
+
+    Example:
+        ```python
+        # Healthy (HTTP 200)
+        {
+          "status": "ok",
+          "fail2ban": "online"
+        }
+
+        # Unhealthy (HTTP 503)
+        {
+          "status": "unavailable",
+          "fail2ban": "offline"
+        }
+        ```
+    """
+
+    status: Literal["ok", "unavailable"] = Field(
+        ...,
+        description="Application health status: 'ok' when healthy, 'unavailable' otherwise.",
+    )
+    fail2ban: Literal["online", "offline"] = Field(
+        ...,
+        description="fail2ban daemon status: 'online' when reachable, 'offline' otherwise.",
+    )
+
+
+class FlushLogsResponse(BanGuiBaseModel):
+    """Standardized response for the flush-logs command endpoint.
+
+    Fields:
+        message: Human-readable result message from fail2ban.
+
+    Example:
+        ```python
+        {"message": "Success: fail2ban log files were flushed."}
+        ```
+    """
+
+    message: str = Field(..., description="Human-readable result message from fail2ban.")