[UX/UI] Optional parameters: Parameter dropdown

### Severity

- P3: Medium (Minor functionality affected)

### MCP Server Creation Source

- MCP Server in API Center

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### Description
Dropdown for optional parameters:
- Add label for dropdown: Parameters
- Placeholder text: Add parameters (Select parameters works too)
- Showing x of y: Do not display in dropdown
- Align dropdown with the other dropdowns and inputs

### Why it matters
- This creates cognitive friction: users have to guess or rely on placeholder text (which isn’t a reliable label).
- This disrupts the predictable scanning pattern (label → input) and creates an awkward gap in the vertical flow, making the form feel broken.
- Without a proper or accessible equivalent (aria-label, aria-labelledby), screen readers can’t describe the field properly.
- This makes the form inaccessible to users with assistive technology.
- May impact task completion rate.

### Screenshot (To-be)

### Screenshot (As-is)