feat(captain): add FAQ suggestion data model

db/migrate/20260710000000_create_captain_faq_suggestions.rb

@@ -0,0 +1,44 @@
+class CreateCaptainFaqSuggestions < ActiveRecord::Migration[7.1]
+  def change
+    create_faq_suggestions
+    create_faq_observations
+  end
+
+  private
+
+  def create_faq_suggestions
+    create_table :captain_faq_suggestions do |t|
+      t.string :question, null: false
+      t.text :answer, null: false
+      t.vector :embedding, limit: 1536
+      t.references :assistant, null: false, index: true
+      t.references :account, null: false, index: true
+      t.integer :source_count, null: false, default: 0
+      t.integer :status, null: false, default: 0
+
+      t.timestamps
+    end
+
+    add_index :captain_faq_suggestions, [:assistant_id, :status]
+    add_index :captain_faq_suggestions, :embedding, using: :ivfflat,
+                                                    name: 'vector_idx_captain_faq_suggestions_embedding',
+                                                    opclass: :vector_cosine_ops
+  end
+
+  def create_faq_observations
+    create_table :captain_faq_observations do |t|
+      t.references :conversation, null: false, index: true
+      t.references :faq_suggestion, index: true
+      t.string :generated_question, null: false
+      t.text :generated_answer, null: false
+      t.integer :status, null: false, default: 0
+
+      t.timestamps
+    end
+
+    add_index :captain_faq_observations, [:conversation_id, :faq_suggestion_id],
+              unique: true,
+              where: 'faq_suggestion_id IS NOT NULL',
+              name: 'idx_captain_faq_observations_on_conversation_and_suggestion'
+  end
+end