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/db/migrations/0006_many_northstar.sql

@@ -0,0 +1,5 @@
+CREATE TABLE `app_settings` (
+	`key` text PRIMARY KEY NOT NULL,
+	`value` text,
+	`updated_at` text NOT NULL
+);

server/db/migrations/meta/_journal.json

@@ -43,6 +43,13 @@
       "when": 1780718324238,
       "tag": "0005_silent_drax",
       "breakpoints": true
+    },
+    {
+      "idx": 6,
+      "version": "6",
+      "when": 1780724800966,
+      "tag": "0006_many_northstar",
+      "breakpoints": true
     }
   ]
 }