refactor: Drop remote_id from authors and series tables

Leftover from the removed WordPress import service. Updated
Author.ransackable_attributes accordingly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: tataihono

app/models/author.rb

@@ -15,6 +15,6 @@ def self.ransackable_associations(_auth_object = nil)
   end
 
   def self.ransackable_attributes(_auth_object = nil)
-    %w[created_at id name remote_id slug updated_at]
+    %w[created_at id name slug updated_at]
   end
 end

db/migrate/20260328103303_remove_remote_id_from_authors_and_series.rb

@@ -0,0 +1,6 @@
+class RemoveRemoteIdFromAuthorsAndSeries < ActiveRecord::Migration[7.2]
+  def change
+    remove_column :authors, :remote_id, :string
+    remove_column :series, :remote_id, :string
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.2].define(version: 2026_03_28_103010) do
+ActiveRecord::Schema[7.2].define(version: 2026_03_28_103303) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_stat_statements"
   enable_extension "pgcrypto"
@@ -64,7 +64,6 @@
     t.string "slug"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.string "remote_id"
   end
 
   create_table "categories", id: :uuid, default: -> { "public.gen_random_uuid()" }, force: :cascade do |t|
@@ -116,7 +115,6 @@
     t.string "slug"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.string "remote_id"
   end
 
   create_table "sermon_authors", id: :uuid, default: -> { "public.gen_random_uuid()" }, force: :cascade do |t|