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/dashboard.html

@@ -13,7 +13,7 @@
             <h1>Felhom Hub</h1>
             <nav class="nav-links">
                 <a href="/" class="nav-link active">Dashboard</a>
-                <a href="/configs" class="nav-link">Configurations</a>
+                <a href="/configs" class="nav-link">Customers</a>
             </nav>
         </header>