refactor: enforce RBAC decorators on all API endpoints

- Add @require_role() decorators to all GET/POST/PUT endpoints
- Centralize role-based access control per memory: RBAC null-role bug required server-side gating
- Admin (manage_admins), Editor (write ops), Viewer (read ops), Public endpoints
- Removes client-side role checks as per memory: server-side UI gating is mandatory

decnet/web/router/fleet/api_mutate_decky.py

@@ -2,7 +2,7 @@ import os
 from fastapi import APIRouter, Depends, HTTPException, Path
 
 from decnet.mutator import mutate_decky
-from decnet.web.dependencies import get_current_user, repo
+from decnet.web.dependencies import require_admin, repo
 
 router = APIRouter()
 
@@ -10,11 +10,11 @@ router = APIRouter()
 @router.post(
     "/deckies/{decky_name}/mutate",
     tags=["Fleet Management"],
-    responses={401: {"description": "Could not validate credentials"}, 404: {"description": "Decky not found"}}
+    responses={401: {"description": "Could not validate credentials"}, 403: {"description": "Insufficient permissions"}, 404: {"description": "Decky not found"}}
 )
 async def api_mutate_decky(
     decky_name: str = Path(..., pattern=r"^[a-z0-9\-]{1,64}$"),
-    current_user: str = Depends(get_current_user),
+    admin: dict = Depends(require_admin),
 ) -> dict[str, str]:
     if os.environ.get("DECNET_CONTRACT_TEST") == "true":
         return {"message": f"Successfully mutated {decky_name} (Contract Test Mock)"}