Fix interest rate validation error in early mortgage payoff calculator

Use tool.interest_rate instead of tool.mortgage_rate_30 to prevent
exceeding the 100% maximum validation constraint.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Shpigford

app/views/tools/widgets/forms/_early_mortgage_payoff_calculator.html.erb

@@ -10,7 +10,7 @@
     <%= form.unit_field :years_left, label: "Years left on loan", value: tool.years_left, label_right: "years", data: { controller: "autonumeric", autonumeric_options_value: { decimalPlaces: 0 }, auto_submit_form_target: "auto" } %>
   </div>
   <div class="flex flex-col gap-2">
-    <%= form.unit_field :interest_rate, label: "Interest rate", value: tool.mortgage_rate_30, label_right: "%", data: { controller: "autonumeric", autonumeric_options_value: { decimalPlaces: 2 }, auto_submit_form_target: "auto" } %>
+    <%= form.unit_field :interest_rate, label: "Interest rate", value: tool.interest_rate * 100, label_right: "%", data: { controller: "autonumeric", autonumeric_options_value: { decimalPlaces: 2 }, auto_submit_form_target: "auto" } %>
   </div>
   <div data-controller="synchronized-input" class="flex flex-col gap-2">
     <%= form.unit_field :extra_payment, label: "Extra monthly payment", value: tool.extra_payment, unit_symbol: "$", data: { controller: "autonumeric", synchronized_input_target: "input", action: "synchronized-input#syncValue input->auto-submit-form#submit", auto_submit_form_target: "auto", autosubmit_trigger_event: "input-sync" } %>