feat(whatsapp-call): add call recording, transcription, beforeunload termination and documentation

db/migrate/20260323100000_add_message_id_to_whatsapp_calls.rb

@@ -0,0 +1,5 @@
+class AddMessageIdToWhatsappCalls < ActiveRecord::Migration[7.1]
+  def change
+    add_reference :whatsapp_calls, :message, null: true, foreign_key: true, index: true
+  end
+end

db/migrate/20260323110000_add_transcript_to_whatsapp_calls.rb

@@ -0,0 +1,5 @@
+class AddTranscriptToWhatsappCalls < ActiveRecord::Migration[7.1]
+  def change
+    add_column :whatsapp_calls, :transcript, :text
+  end
+end