fix: Separate settings groups to prevent cross-tab overwrites (v0.4.5)

Split Metrics sub-tab settings into separate WordPress option groups:
- wp_prometheus_endpoint_settings for auth token
- wp_prometheus_selection_settings for enabled metrics
- wp_prometheus_advanced_settings for isolated mode

This fixes the bug where saving from one sub-tab would clear settings
from other sub-tabs due to all settings sharing a single option group.

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

src/Metrics/Collector.php

@@ -121,14 +121,62 @@ class Collector {
         /**
          * Fires after default metrics are collected.
          *
-         * Skip in early metrics mode to avoid triggering third-party hooks
-         * that may cause recursion issues (e.g., Twig-based plugins).
+         * In isolated mode, skip custom hooks to avoid any potential issues.
+         * In safe mode (default), fire hooks with protection against recursion.
          *
          * @param Collector $collector The metrics collector instance.
          */
-        if ( ! defined( 'WP_PROMETHEUS_EARLY_METRICS' ) || ! WP_PROMETHEUS_EARLY_METRICS ) {
-            do_action( 'wp_prometheus_collect_metrics', $this );
+        if ( defined( 'WP_PROMETHEUS_ISOLATED_MODE' ) && WP_PROMETHEUS_ISOLATED_MODE ) {
+            // Isolated mode: skip all third-party hooks for maximum safety.
+            return;
         }
+
+        // Safe mode: fire custom hooks with protection.
+        $this->fire_custom_metrics_hook();
+    }
+
+    /**
+     * Fire custom metrics hook with protection against recursion.
+     *
+     * Removes potentially problematic filters, uses output buffering,
+     * and catches any errors from third-party plugins.
+     *
+     * @return void
+     */
+    private function fire_custom_metrics_hook(): void {
+        // Remove content filters again (in case any plugin re-added them).
+        if ( function_exists( 'wp_prometheus_remove_content_filters' ) ) {
+            wp_prometheus_remove_content_filters();
+        } else {
+            // Fallback if function doesn't exist.
+            remove_all_filters( 'the_content' );
+            remove_all_filters( 'the_excerpt' );
+            remove_all_filters( 'get_the_excerpt' );
+            remove_all_filters( 'the_title' );
+        }
+
+        // Use output buffering to prevent any accidental output from plugins.
+        ob_start();
+
+        try {
+            /**
+             * Fires after default metrics are collected.
+             *
+             * Third-party plugins can use this hook to add custom metrics.
+             *
+             * @param Collector $collector The metrics collector instance.
+             */
+            do_action( 'wp_prometheus_collect_metrics', $this );
+        } catch ( \Throwable $e ) {
+            // Log the error but don't let it break metrics output.
+            if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+                // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+                error_log( 'WP Prometheus: Error in custom metrics hook: ' . $e->getMessage() );
+            }
+        }
+
+        // Discard any output from plugins.
+        ob_end_clean();
     }
 
     /**