feat(services): cleanup, services admin UI, docs

PR 4a of the runtime service registry change.

- Remove addon pages (/addons/:addonId, AddonPage, addons/*) superseded by
  service pages.
- Remove grafana_url/prometheus_url from backend config, compose, .env.example,
  and README (URLs now live on service records; VITE_ frontend deep-link vars
  retained).
- Add Services page (/services) with create/list/delete + sidebar nav, so
  services are configurable in the tool itself and service pages are reachable.
- Update docs/REQUIREMENTS.md service-registry section; add CHANGELOG.md with
  the breaking-upgrade note (MANAGE_ENCRYPTION_KEY required; grafana/prometheus
  env vars removed; default widget seeding removed).

Verification: backend ruff clean, pytest 222 passed; frontend lint 0 errors,
build success, 70 tests passed.

frontend/src/App.tsx

@@ -22,8 +22,8 @@ import { FileBrowser } from "./pages/FileBrowser";
 import { Actions } from "./pages/Actions";
 import BackupsPage from "./components/BackupsPage";
 import { ObservabilityPage } from "./components/ObservabilityPage";
-import { AddonPage } from "./pages/AddonPage";
 import { ServicePage } from "./pages/ServicePage";
+import { ServicesPage } from "./pages/ServicesPage";
 import { getOidcConfig, isOidcConfigured, setAccessToken } from "./auth";
 import { fetchAppVersion } from "./api/client";
 import { FRONTEND_VERSION_LABEL } from "./version";
@@ -57,6 +57,7 @@ import {
 	LogOut,
 	ChevronLeft,
 	ChevronRight,
+	Boxes,
 } from "lucide-react";
 
 const queryClient = new QueryClient({
@@ -90,6 +91,7 @@ const navItems = [
 	{ path: "/backups", label: "Backups", icon: DatabaseBackup },
 	{ path: "/users", label: "Users", icon: Users },
 	{ path: "/actions", label: "Actions", icon: Zap },
+	{ path: "/services", label: "Services", icon: Boxes },
 	{ path: "/settings", label: "Settings", icon: SettingsIcon },
 ];
 
@@ -451,11 +453,8 @@ function AppInner() {
 								<Route path="/backups" element={<BackupsPage />} />
 								<Route path="/observability" element={<ObservabilityPage />} />
 								<Route path="/settings" element={<Settings />} />
-								<Route path="/addons/:addonId" element={<AddonPage />} />
-								<Route
-									path="/services/:serviceType/:serviceId"
-									element={<ServicePage />}
-								/>
+								<Route path="/services" element={<ServicesPage />} />
+								<Route path="/services/:serviceType/:serviceId" element={<ServicePage />} />
 							</Route>
 						</Routes>
 					</BrowserRouter>
@@ -487,11 +486,8 @@ function AppInner() {
 							<Route path="/backups" element={<BackupsPage />} />
 							<Route path="/observability" element={<ObservabilityPage />} />
 							<Route path="/settings" element={<Settings />} />
-							<Route path="/addons/:addonId" element={<AddonPage />} />
-							<Route
-								path="/services/:serviceType/:serviceId"
-								element={<ServicePage />}
-							/>
+							<Route path="/services" element={<ServicesPage />} />
+							<Route path="/services/:serviceType/:serviceId" element={<ServicePage />} />
 						</Route>
 					</Routes>
 				</BrowserRouter>