Wiki 依存の排除 (#431) (#432)

Reviewed-on: #432
Co-authored-by: miteruzo <miteruzo@naver.com>

backend/db/migrate/20261015000000_drop_wiki_pages.rb

@@ -0,0 +1,9 @@
+class DropWikiPages < ActiveRecord::Migration[8.0]
+  def change
+    drop_table :wiki_versions
+    drop_table :wiki_revision_lines
+    drop_table :wiki_lines
+    drop_table :wiki_revisions
+    drop_table :wiki_pages
+  end
+end

backend/db/migrate/20261015003000_remove_tag_name_id_from_tags.rb

@@ -0,0 +1,11 @@
+class RemoveTagNameIdFromTags < ActiveRecord::Migration[8.0]
+  def up
+    remove_foreign_key :tags, column: :tag_name_id
+    remove_foreign_key :tag_names, column: :canonical_id
+
+    remove_column :tags, :tag_name_id
+    remove_column :tag_names, :canonical_id
+  end
+
+  def down = raise ActiveRecord::IrreversibleMigration, '戻せません．'
+end

backend/db/migrate/20261015010000_delete_name_for_wiki_from_tag_names.rb

@@ -0,0 +1,15 @@
+class DeleteNameForWikiFromTagNames < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      DELETE
+      FROM
+        tag_names
+      WHERE
+        tag_id IS NULL
+    SQL
+
+    change_column_null :tag_names, :tag_id, false
+  end
+
+  def down = raise ActiveRecord::IrreversibleMigration, '戻せません．'
+end