Use dependent: :purge_later for ActiveRecord attachments (#882)

* Use dependent: :purge_later for user profile_image cleanup

This is a simpler alternative to PR #787's callback-based approach.
Instead of adding a custom callback and method, we use Rails' built-in
`dependent: :purge_later` option which is already used by FamilyExport
and other models in the codebase.

This single-line change ensures orphaned ActiveStorage attachments are
automatically purged when a user is destroyed, without the overhead of
querying all attachments manually.

https://claude.ai/code/session_01Np3deHEAJqCBfz3aY7c3Tk

* Add dependent: :purge_later to all ActiveStorage attachments

Extends the attachment cleanup from PR #787 to cover ALL models with
ActiveStorage attachments, not just User.profile_image.

Models updated:
- PdfImport.pdf_file - prevents orphaned PDF files from imports
- Account.logo - prevents orphaned account logos
- PlaidItem.logo, SimplefinItem.logo, SnaptradeItem.logo,
  CoinstatsItem.logo, CoinbaseItem.logo, LunchflowItem.logo,
  MercuryItem.logo, EnableBankingItem.logo - prevents orphaned
  provider logos

This ensures that when a family is deleted (cascade from last user
purge), all associated storage files are properly cleaned up via
Rails' built-in dependent: :purge_later mechanism.

https://claude.ai/code/session_01Np3deHEAJqCBfz3aY7c3Tk

* Make sure `Provider` generator adds it

* Fix tests

---------

Co-authored-by: Claude <noreply@anthropic.com>

test/models/account_test.rb

@@ -1,7 +1,7 @@
 require "test_helper"
 
 class AccountTest < ActiveSupport::TestCase
-  include SyncableInterfaceTest, EntriesTestHelper
+  include SyncableInterfaceTest, EntriesTestHelper, ActiveJob::TestHelper
 
   setup do
     @account = @syncable = accounts(:depository)
@@ -155,4 +155,21 @@ class AccountTest < ActiveSupport::TestCase
     assert @account.taxable?
     assert_not @account.tax_advantaged?
   end
+
+  test "destroying account purges attached logo" do
+    @account.logo.attach(
+      io: StringIO.new("fake-logo-content"),
+      filename: "logo.png",
+      content_type: "image/png"
+    )
+
+    attachment_id = @account.logo.id
+    assert ActiveStorage::Attachment.exists?(attachment_id)
+
+    perform_enqueued_jobs do
+      @account.destroy!
+    end
+
+    assert_not ActiveStorage::Attachment.exists?(attachment_id)
+  end
 end