docs: add OpenAPI responses={} to all router endpoints

Add explicit HTTP status code documentation to every endpoint
across 15 router files. Each endpoint now declares all possible
response codes (200/201/204/400/401/404/409/429/502/503) with
descriptions so frontend can distinguish error types.

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

backend/app/routers/action_config.py

@@ -128,6 +128,11 @@ _NamePath = Annotated[
     "",
     response_model=ActionListResponse,
     summary="List all available actions with active/inactive status",
+    responses={
+        200: {"description": "Action list returned", "model": ActionListResponse},
+        401: {"description": "Session missing, expired, or invalid"},
+        502: {"description": "fail2ban unreachable"},
+    },
 )
 async def list_actions(
     request: Request,
@@ -165,6 +170,12 @@ async def list_actions(
     "/{name}",
     response_model=ActionConfig,
     summary="Return full parsed detail for a single action",
+    responses={
+        200: {"description": "Action config returned", "model": ActionConfig},
+        401: {"description": "Session missing, expired, or invalid"},
+        404: {"description": "Action not found in action.d/"},
+        502: {"description": "fail2ban unreachable"},
+    },
 )
 async def get_action(
     request: Request,
@@ -205,6 +216,14 @@ async def get_action(
     response_model=ActionConfig,
     summary="Update an action's .local override with new lifecycle command values",
     dependencies=[Depends(_check_action_update_rate_limit)],
+    responses={
+        200: {"description": "Action updated", "model": ActionConfig},
+        400: {"description": "Invalid action name"},
+        401: {"description": "Session missing, expired, or invalid"},
+        404: {"description": "Action not found"},
+        429: {"description": "Rate limit exceeded for action update operations"},
+        500: {"description": "Failed to write .local file"},
+    },
 )
 async def update_action(
     request: Request,
@@ -246,6 +265,14 @@ async def update_action(
     status_code=status.HTTP_201_CREATED,
     summary="Create a new user-defined action",
     dependencies=[Depends(_check_action_create_rate_limit)],
+    responses={
+        201: {"description": "Action created", "model": ActionConfig},
+        400: {"description": "Invalid action name"},
+        401: {"description": "Session missing, expired, or invalid"},
+        409: {"description": "Action already exists"},
+        429: {"description": "Rate limit exceeded for action create operations"},
+        500: {"description": "Failed to write .local file"},
+    },
 )
 async def create_action(
     request: Request,
@@ -284,6 +311,15 @@ async def create_action(
     status_code=status.HTTP_204_NO_CONTENT,
     summary="Delete a user-created action's .local file",
     dependencies=[Depends(_check_action_delete_rate_limit)],
+    responses={
+        204: {"description": "Action deleted successfully"},
+        400: {"description": "Invalid action name"},
+        401: {"description": "Session missing, expired, or invalid"},
+        404: {"description": "Action not found"},
+        409: {"description": "Action is a shipped default (conf-only)"},
+        429: {"description": "Rate limit exceeded for action delete operations"},
+        500: {"description": "Failed to delete .local file"},
+    },
 )
 async def delete_action(
     request: Request,