feat: add a runtime diagnostics page

Adds GET /api/clouds/:cloud/diagnostics and a Diagnostics page in the
General nav. The report combines, in one call:

- runtime reachability, latency, version and edition from /_floci/health
- every service the runtime emulates, with the console pages backed by it
- per-console-service probes (the existing status check)
- EC2 instance containers from /_floci/diagnose
- console uptime, sign-in mode and active session count

Each source is optional, so a down runtime still yields a partial report.

packages/frontend/src/components/Layout.tsx

@@ -1,5 +1,5 @@
 import {NavLink, Outlet, useLocation, useSearchParams} from 'react-router-dom'
-import {AlertTriangle, ChevronsLeft, ChevronsRight, LayoutDashboard, LogOut, Moon, Search, Sun, Terminal} from 'lucide-react'
+import {Activity, AlertTriangle, ChevronsLeft, ChevronsRight, LayoutDashboard, LogOut, Moon, Search, Sun, Terminal} from 'lucide-react'
 import {useCallback, useEffect, useRef, useState} from 'react'
 import theCloud from '../../../../TheCloud.png'
 import {useTheme} from '@/lib/useTheme'
@@ -184,6 +184,7 @@ export function Layout() {
                         <div className="nav-section">
                             <span className="nav-label">General</span>
                             <NavItem to={`/console/${activeCloud}`} icon={<LayoutDashboard size={18} aria-hidden="true"/>} label="Console Home" collapsed={collapsed}/>
+                            <NavItem to={`/diagnostics/${activeCloud}`} icon={<Activity size={18} aria-hidden="true"/>} label="Diagnostics" collapsed={collapsed}/>
                         </div>
                         <CloudServiceNav collapsed={collapsed}/>
                     </nav>
@@ -356,6 +357,6 @@ function TopbarSearch() {
 }
 
 function activeCloudFromPath(pathname: string): 'aws' | 'azure' | 'gcp' {
-    const match = pathname.match(/^\/(?:cloud-explorer|console)\/(aws|azure|gcp)(?:\/|$)/)
+    const match = pathname.match(/^\/(?:cloud-explorer|console|diagnostics)\/(aws|azure|gcp)(?:\/|$)/)
     return (match?.[1] ?? 'aws') as 'aws' | 'azure' | 'gcp'
 }