feat: merge report-only customers into Customers page, rename tab

- Customers page now shows ALL customers: both pre-configured (managed)
  and report-only (manual) — merged from customer_configs + reports tables
- Renamed "Configurations" → "Customers" in navigation tabs
- Renamed "+ New Configuration" → "+ Add Customer"
- Status column with ok/warn/down badges, version column, managed/manual badge

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

hub/internal/web/templates/config_detail.html

@@ -12,11 +12,11 @@
             <h1>Felhom Hub</h1>
             <nav class="nav-links">
                 <a href="/" class="nav-link">Dashboard</a>
-                <a href="/configs" class="nav-link active">Configurations</a>
+                <a href="/configs" class="nav-link active">Customers</a>
             </nav>
         </header>
 
-        <a href="/configs" class="back-link">&larr; All Configurations</a>
+        <a href="/configs" class="back-link">&larr; All customers</a>
 
         {{if .Flash}}
         <div class="flash flash-success">
@@ -123,7 +123,7 @@
         </div>
 
         <footer>
-            <p>Felhom Hub — Configuration Management</p>
+            <p>Felhom Hub — Customer Management</p>
         </footer>
     </div>