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/prometheus/prometheus.yml.j2

@@ -0,0 +1,48 @@
+global:
+  scrape_interval: {{ prometheus_scrape_interval }}
+  evaluation_interval: {{ prometheus_evaluation_interval }}
+
+alerting:
+  alertmanagers:
+    - static_configs:
+        - targets:
+          - {{ alertmanager_host }}:{{ alertmanager_port }}
+
+rule_files:
+  - "alert_rules.yml"
+
+scrape_configs:
+  - job_name: 'prometheus'
+    static_configs:
+      - targets: ['localhost:9090']
+
+  - job_name: 'node-exporter'
+    static_configs:
+      - targets: {{ prometheus_targets | to_json }}
+
+  - job_name: 'alertmanager'
+    static_configs:
+      - targets: ['{{ alertmanager_host }}:{{ alertmanager_port }}']
+
+  - job_name: 'haproxy'
+    static_configs:
+      - targets: ['titania.incus:8404']
+    metrics_path: '/metrics'
+
+  - job_name: 'gitea'
+    static_configs:
+      - targets: ['oberon.incus:22084']
+    metrics_path: '/metrics'
+    authorization:
+      type: Bearer
+      credentials: '{{ vault_gitea_metrics_token }}'
+
+  - job_name: 'casdoor'
+    static_configs:
+      - targets: ['{{ casdoor_metrics_host }}:{{ casdoor_metrics_port }}']
+    metrics_path: '/api/metrics'
+    params:
+      accessKey: ['{{ casdoor_prometheus_access_key }}']
+      accessSecret: ['{{ casdoor_prometheus_access_secret }}']
+
+# Red Panda Approved Prometheus Configuration