Resolve adminV2 skipped tests

[americac]

• Fixed 29 previously skipped admin_v2 controller tests that were
  disabled after a Rails upgrade
• Fixed bugs in form builder, controllers, and models that were causing
  test failures
• All 687 tests now pass with 0 failures and 0 errors

Changes

Bug Fixes

Form Builder (app/form_builders/admin_v2/form_builder.rb)

• Fixed input_class and error_message methods to handle nil objects
  using safe navigation, preventing crashes when forms are created
  without a model
• Enhanced association_select to support callable label_method
  (lambdas/procs) in addition to symbols

Teachers Controller (app/controllers/admin_v2/teachers_controller.rb)

• Fixed teacher_params to properly permit classroom_ids as an array
  parameter
• Changed destroy action to use discard for soft delete consistency
  with other user types

SchoolYear Model (app/models/school_year.rb)

• Added uniqueness validation for year_id scoped to school_id to catch
  duplicates at the model level
• Changed dependent: :restrict_with_error to dependent:
  :restrict_with_exception so the controller's rescue block properly
  handles deletion restrictions

Portfolio Transactions View
(app/views/admin_v2/portfolio_transactions/show.html.erb)

• Fixed invalid route helper admin_v2_portfolio_path that doesn't exist

Test Fixes

• grades_controller_test.rb: Removed unnecessary skips (tests were
  passing)
• students_controller_test.rb: Fixed assertions to match actual view
  content and enum values
• teachers_controller_test.rb: Updated for soft delete behavior and
  classroom associations
• school_years_controller_test.rb: Fixed assertion syntax and test
  expectations
• portfolio_transactions_controller_test.rb: Removed skips (working
  after form builder fix)
  - base_controller_test.rb: Rewrote sorting tests to use proper HTTP
  integration tests
• school_year_test.rb: Updated to expect DeleteRestrictionError
  exception

Notes

• Discuss new or non-trivial changes in #stocks-in-the-future slack channel before or during implementation.

[AbuMareBear]

Looks like we worked on the same problem. #1009