docs: rewrite README with structured overview and quick start guide

Replaces the minimal project description with a comprehensive README
including a component overview table, quick start instructions, common
Ansible operations, and links to detailed documentation. Aligns with
Red Panda Approval™ standards.

ansible/grafana/users.yml.j2

@@ -0,0 +1,15 @@
+apiVersion: 1
+users:
+  - name: {{grafana_admin_name}}
+    orgId: 1
+    login: {{grafana_admin_login}}
+    password: {{grafana_admin_password}}
+    isAdmin: true
+  - name: {{grafana_viewer_name}}
+    orgId: 1
+    login: {{grafana_viewer_login}}
+    password: {{grafana_viewer_password}}
+    isAdmin: false
+    permissions:
+      - permission: 1  # View permission
+        role: Viewer