feat: Reorganize settings page with tabbed interface (v0.1.1)

- Add tabbed navigation (License, Metrics, Help)
- Move Prometheus configuration to dedicated Help tab
- Separate static and runtime metrics with descriptions
- Add admin CSS for tab styling
- Add endpoint info, curl examples, and metrics reference in Help tab

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

assets/css/admin.css

@@ -0,0 +1,47 @@
+/**
+ * WP Prometheus Admin Styles
+ *
+ * @package WP_Prometheus
+ */
+
+/* Tab content styling */
+.wp-prometheus-tab-content {
+    margin-top: 20px;
+}
+
+/* License status box */
+.wp-prometheus-license-status {
+    margin: 15px 0;
+}
+
+/* Help tab code blocks */
+.wp-prometheus-tab-content pre {
+    background: #f1f1f1;
+    padding: 15px;
+    overflow-x: auto;
+    margin: 15px 0;
+    border-radius: 3px;
+    border: 1px solid #ddd;
+}
+
+/* Help tab tables */
+.wp-prometheus-tab-content .widefat {
+    margin: 15px 0;
+}
+
+.wp-prometheus-tab-content .widefat code {
+    background: none;
+    padding: 0;
+}
+
+/* Metrics fieldset */
+.wp-prometheus-tab-content fieldset p strong {
+    display: block;
+    margin-bottom: 8px;
+    font-size: 14px;
+}
+
+/* Form table adjustments for tabs */
+.wp-prometheus-tab-content .form-table {
+    margin-top: 10px;
+}