feat: add Grafana dashboard provisioning infrastructure (refs #106)

Add file-based dashboard provisioning config and mount dashboards
directory into Grafana container for auto-loading dashboard JSON files.

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

config/grafana/provisioning/dashboards.yml

@@ -0,0 +1,11 @@
+apiVersion: 1
+providers:
+  - name: 'MotoVaultPro'
+    orgId: 1
+    folder: 'MotoVaultPro'
+    type: file
+    disableDeletion: false
+    updateIntervalSeconds: 30
+    allowUiUpdates: false
+    options:
+      path: /var/lib/grafana/dashboards