Align S-Group subtype combobox width and default option visibility

[Copilot]

How the feature works? / How did you fix the issue?

• Problem: In the S-Group Properties dialog, the Subtype combobox rendered narrower than Type/Repeat pattern when selecting Copolymer, and the default “Not Specified” value appeared blank when selected.
• Changes
  • UI: Apply full-width combobox styling to the Subtype control to match peer inputs and render empty-value (“Not Specified”) selections visibly.
  • Tests: Added a unit test for empty-value option display in the Select component.
  • QA asset: Updated visual confirmation (see https://github.com/user-attachments/assets/0cf4a69a-9b22-4794-866f-7ae484668d9b).

Check list

• unit-tests written
• e2e-tests written
• documentation updated
• PR name follows the pattern #1234 – issue name
• branch name doesn't contain '#'
• PR is linked with the issue
• base branch (master or release/xx) is correct
• task status changed to "Code review"
• reviewers are notified about the pull request

Original prompt

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This section details on the original issue you should resolve

<issue_title>Subtype combo box width is less than other combo boxes on S-Group Properties dialog</issue_title>
<issue_description>Steps to Reproduce

1. Open Molecules mode (clean canvas)
2. Load following SMILES: CCCCC

3. Select whole molecule

4. Press S-Group button (or Ctrl+G keyboard shortcut) to open S-Group Properties dialog
5. Change Type combo box value to Copolymer

Actual behavior
Subtype combo box width is less than other combo boxes

Expected behavior
Subtype combo box width is equal to Type and Repeat pattern combo boxes

Environment details:

• Ketcher Version 3.11.0-rc.1 2025-11-27; 18:06:40
• Indigo Version 1.39.0-rc.1.0-gddb882b27-wasm32-wasm-clang-19.0.0
• Chrome Version 142.0.7444.176 (Official Build) (64-bit)
• Win10</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Subtype combo box width is less than other combo boxes on S-Group Properties dialog #8978

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[AlexeyGirin]

@copilot you did changes in right direction but when I open S-Group dialog the default value (Not Specified) is not visible if selected. It is present in combo box list but if I select it - selected value remain blank. All other values are visible if selected. Please make it visible as well as other values from the list

[Copilot]

@copilot you did changes in right direction but when I open S-Group dialog the default value (Not Specified) is not visible if selected. It is present in combo box list but if I select it - selected...

Fixed. The “Not Specified” option now shows when selected. Screenshot: https://github.com/user-attachments/assets/0cf4a69a-9b22-4794-866f-7ae484668d9b