Implement Student Portfolio Transaction Management

[americac]

!!! Blocked By: #941 !!!

Description:
Add portfolio transaction form to student edit page for adding funds/debits.

Tasks:

• Update Admin::StudentsController:
  • Add add_transaction action
  • Validate transaction params (amount > 0, transaction_type presence, etc.)
  • Create PortfolioTransaction through student's portfolio
  • Handle errors and display meaningful messages
  • Redirect back to edit page with flash
• Update student form view:
  • Add transaction section (only on edit, not new)
  • Display current cash balance (read-only)
  • Add transaction type select (deposit/debit)
  • Add amount field with decimal support
  • Add reason select (uses PortfolioTransaction.reasons enum)
  • Add description textarea
  • Submit to add_transaction action
• Add routes for add_transaction member action

Acceptance Criteria:

• Transaction form only appears on edit page
• Current cash balance displays correctly
• Transaction type select has deposit/debit options
• Amount field validates > 0
• Reason select populates from enum
• Description field optional
• Transaction creates successfully
• Portfolio balance updates correctly
• Validation errors display inline
• Success message confirms transaction
• Form clears after successful transaction

Files to Update:

• app/views/admin/students/_form.html.erb

Reference:

• app/controllers/admin/students_controller.rb (lines 65-96)
• app/views/admin/students/_form.html.erb (lines 64-111)
• app/models/portfolio_transaction.rb (for reasons enum)