feat: implement API versioning /api/v1/

- All backend routers moved to /api/v1/ prefix
- Frontend BASE_URL updated to /api/v1
- Setup redirect middleware updated to redirect to /api/v1/setup
- Health router path fixed: prefix=/api/v1/health, @router.get('')
- conftest.py: set server_status=online for test fixture
- Created Docs/API_VERSIONING.md with deprecation policy
- Updated Docs/Backend-Development.md with versioning section
- Updated Instructions.md curl examples

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

frontend/src/api/client.ts

@@ -17,8 +17,8 @@
 import { ErrorResponse } from "../types/response";
 import { ENDPOINTS } from "./endpoints";
 
-/** Base URL for all API calls. Falls back to `/api` in production. */
-const BASE_URL: string = import.meta.env.VITE_API_URL ?? "/api";
+/** Base URL for all API calls. Falls back to `/api/v1` in production. */
+const BASE_URL: string = import.meta.env.VITE_API_URL ?? "/api/v1";
 
 /** Standard header name for correlation IDs (matches backend convention) */
 const CORRELATION_ID_HEADER: string = "X-Correlation-ID";

frontend/src/api/endpoints.ts

@@ -107,7 +107,7 @@ export const ENDPOINTS = {
   configAction: (name: string): string => `/config/actions/${encodeURIComponent(name)}`,
   configActionRaw: (name: string): string => `/config/actions/${encodeURIComponent(name)}/raw`,
   configActionParsed: (name: string): string =>
-    `/config/actions/${encodeURIComponent(name)}/parsed`,
+    `/config/actions/${encodeURIComponent(name)}/parsed",
 
   // fail2ban log viewer (Task 2)
   configFail2BanLog: "/config/fail2ban-log",