fix(forms): Fix checkbox export values and wide dropdown options

[balazs-szucs]

Description of Changes

Improves the logic for handling checkbox fields in the making more accurate state determination based on the exportValue property

Changes:

• Updated checkbox checked state logic in both FieldInput.tsx and FormFieldOverlay.tsx to check if the value matches the widget's exportValue when present, improving accuracy for custom checkbox values.
• Set the minWidth of select elements to 100% in FormFieldOverlay.tsx to ensure consistent layout and alignment.

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Checklist

General

• I have read the Contribution Guidelines
• I have read the Stirling-PDF Developer Guide (if applicable)
• I have read the How to add new languages to Stirling-PDF (if applicable)
• I have performed a self-review of my own code
• My changes generate no new warnings

Documentation

• I have updated relevant docs on Stirling-PDF's doc repo (if functionality has heavily changed)
• I have read the section Add New Translation Tags (for new translation tags only)

Translations (if applicable)

• I ran scripts/counter_translation.py

UI Changes (if applicable)

• Screenshots or videos demonstrating the UI changes are attached (e.g., as comments or direct attachments in the PR)

Testing (if applicable)

• I have run task check to verify linters, typechecks, and tests pass
• I have tested my changes locally. Refer to the Testing Guide for more details.

[Copilot]

Pull request overview

Updates the form-fill UI’s checkbox handling to better respect per-widget exportValue when determining checked state, and improves select/dropdown layout by forcing a full-width minimum size in the overlay.

Changes:

• Update checkbox checked-state logic in FieldInput and FormFieldOverlay to compare against exportValue when present.
• Set overlay <select> styling to minWidth: 100% to prevent narrow dropdown rendering.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
frontend/editor/src/core/tools/formFill/FormFieldOverlay.tsx	Adjusts overlay checkbox checked-state logic to prefer exportValue; makes dropdowns consistently wide via minWidth: 100%.
frontend/editor/src/core/tools/formFill/FieldInput.tsx	Adjusts sidebar/field-list checkbox checked-state logic to prefer exportValue.

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