feat(api): profil machine éditable, sonde, et réglages globaux apt-cacher-ng

- machines : updateMachine (PATCH /machines/:id) + POST /machines/:id/probe
  (sonde synchrone → faits + proposition de correction) ; MachineView expose
  machineKind/virtualization ; CreateMachineInput accepte aptProxyMode persistent
- app_settings (clé/valeur, migration 0006) + service appSettings :
  défaut apt-cacher-ng (mode + url) ; applyProxyToAllMachines
- routes /settings : GET, PUT /apt-proxy, POST /apt-proxy/apply-all

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/services/appSettings.ts

@@ -0,0 +1,43 @@
+// server/services/appSettings.ts
+import { db, schema } from "../db/client.js";
+import type { AptProxyMode } from "@shared/types.js";
+
+export const SETTING_KEYS = {
+  defaultAptProxyUrl: "default_apt_proxy_url",
+  defaultAptProxyMode: "default_apt_proxy_mode",
+} as const;
+
+export function getAllSettings(): Record<string, string> {
+  return Object.fromEntries(
+    db.select().from(schema.appSettings).all().map((r) => [r.key, r.value ?? ""]),
+  );
+}
+
+export function setSettings(patch: Record<string, string | null>): void {
+  const now = new Date().toISOString();
+  for (const [key, value] of Object.entries(patch)) {
+    db.insert(schema.appSettings)
+      .values({ key, value, updatedAt: now })
+      .onConflictDoUpdate({ target: schema.appSettings.key, set: { value, updatedAt: now } })
+      .run();
+  }
+}
+
+export interface DefaultAptProxy {
+  mode: AptProxyMode;
+  url: string | null;
+}
+
+export function getDefaultAptProxy(): DefaultAptProxy {
+  const s = getAllSettings();
+  const mode = (s[SETTING_KEYS.defaultAptProxyMode] as AptProxyMode) || "direct";
+  return { mode, url: s[SETTING_KEYS.defaultAptProxyUrl] || null };
+}
+
+export function setDefaultAptProxy(input: DefaultAptProxy): DefaultAptProxy {
+  setSettings({
+    [SETTING_KEYS.defaultAptProxyMode]: input.mode,
+    [SETTING_KEYS.defaultAptProxyUrl]: input.url ?? "",
+  });
+  return getDefaultAptProxy();
+}