hub v0.1.7: Infrastructure backup endpoints for disaster recovery

Add infra-backup push/pull API for controller DR:
- POST /api/v1/infra-backup — controller pushes infrastructure snapshot
- GET /api/v1/infra-backup/{customer_id} — fresh controller pulls backup
- infra_backups SQLite table with per-customer snapshots
- Customer detail page shows infra backup status card
- README.md with full API docs and DR flow

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

hub/internal/web/templates/customer.html

@@ -127,6 +127,29 @@
             {{end}}
         </section>
 
+        <!-- Infra Backup (Disaster Recovery) -->
+        <section class="card">
+            <h2>Infra Backup</h2>
+            {{if .InfraBackup}}
+            <div class="info-grid">
+                <div class="info-item">
+                    <span class="label">Last Updated</span>
+                    <span class="value">{{.InfraBackupAge}}</span>
+                </div>
+                <div class="info-item">
+                    <span class="label">Deployed Stacks</span>
+                    <span class="value">{{.InfraBackup.StackCount}}</span>
+                </div>
+                <div class="info-item">
+                    <span class="label">Disks</span>
+                    <span class="value">{{.InfraBackup.DiskCount}}</span>
+                </div>
+            </div>
+            {{else}}
+            <p style="color: #facc15">No infra backup received yet</p>
+            {{end}}
+        </section>
+
         <!-- Health -->
         <section class="card">
             <h2>Health</h2>