fix: wire is_hard_drop_enabled + drop_score_threshold settings into Classifier filter chain

Settings::register_classifier_filters() registers priority-5 callbacks on
cf7stg_classifier_thresholds and cf7stg_hard_drop_rules so the UI options
actually influence Classifier behaviour. Called from Plugin::boot(). User
filters at priority 10 override these defaults as expected. Adds 4 tests
covering the wired behaviour and override priority. Also adds dry_run_drop?
to MessageFormatter::build() @param docblock.

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

includes/class-message-formatter.php

@@ -24,7 +24,8 @@ final class MessageFormatter
      *   reason:string,
      *   ip:string,
      *   user_agent:string,
-     *   is_retro:bool
+     *   is_retro:bool,
+     *   dry_run_drop?:bool
      * } $ctx
      *
      * @return array{text:string,reply_markup:array|null}

includes/class-plugin.php

@@ -43,6 +43,9 @@ final class Plugin
 
     public function boot(): void
     {
+        // Inject silent-drop options into Classifier filter chain
+        Settings::register_classifier_filters();
+
         // Register runtime hooks
         Dispatcher::register_hooks();
         (new CF7Source())->register();

includes/class-settings.php

@@ -171,4 +171,27 @@ final class Settings
             'reset_at'       => $today,
         ];
     }
+
+    /**
+     * Register default callbacks that inject silent-drop options into the
+     * Classifier's filter chain. Runs at plugin boot. User filters at the
+     * default priority (10) override these (priority 5).
+     */
+    public static function register_classifier_filters(): void
+    {
+        add_filter('cf7stg_classifier_thresholds', static function ($thresholds) {
+            if (is_array($thresholds)) {
+                $thresholds['drop'] = self::get_drop_score_threshold();
+            }
+            return $thresholds;
+        }, 5);
+
+        add_filter('cf7stg_hard_drop_rules', static function ($rules) {
+            if (is_array($rules) && !self::is_hard_drop_enabled()) {
+                $rules['short_latin_name']   = false;
+                $rules['placeholder_fields'] = false;
+            }
+            return $rules;
+        }, 5);
+    }
 }