feat: add Services and Logs modules (systemctl + journalctl via SSH)

Backend:
- modules/services: list, status, start/stop/restart systemctl services
  with pct exec support for LXC targets
- modules/logs: journalctl unit listing + WebSocket live streaming
  (direct SSH connection, journalctl -f, graceful teardown on WS close)
- migrations/003: seed services and logs modules in DB
- main.go: register services.New() and logs.New() in module loader

Frontend:
- services.html: target selector, search/filter, services table with
  active state indicators and start/stop/restart buttons
- logs.html: target + unit selectors, live follow toggle, scrollable
  terminal output with 3000-line cap
- app.js: servicePage() and logsPage() Alpine components + navItems
- locales: services and logs i18n keys (fr + en)
- pages.css: services table, state dots, logs output styles

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/locales/en.json

@@ -115,6 +115,34 @@
     "desc": "SFTP file browser",
     "moduleNotEnabled": "Module not enabled. Go to Settings → Modules to enable it."
   },
+  "services": {
+    "desc": "systemd service management",
+    "target": "Target",
+    "filter": "Filter by name or description…",
+    "noServices": "No services found",
+    "name": "Service",
+    "status": "Status",
+    "substate": "Sub-state",
+    "description": "Description",
+    "start": "Start",
+    "stop": "Stop",
+    "restart": "Restart",
+    "reload": "Reload",
+    "enable": "Enable",
+    "disable": "Disable"
+  },
+  "logs": {
+    "desc": "System journal viewer via journalctl",
+    "target": "Target",
+    "unit": "Unit",
+    "unitAll": "All units",
+    "lines": "Lines",
+    "follow": "Follow live",
+    "stopFollow": "Stop",
+    "clear": "Clear",
+    "noLogs": "No logs — click «Follow» to start",
+    "connecting": "Connecting…"
+  },
   "settings": {
     "general": "General",
     "infrastructure": "Infrastructure",