FLOW-2583: Fix prompt box toolbar layout, icon size, and dropdown behavior - (Jira Coding Agent)

[atlassian]

This PR addresses UI issues in the prompt box related to toolbar layout, icon sizing, and dropdown behavior.

Key Changes

Area	Change Description
Toolbar Layout	Prevent toolbar in the prompt box from breaking into multiple lines in narrow sidebars by disabling flex wrapping and adjusting layout styles.
Icon Sizing	Reduce sizes of prompt box toolbar buttons and icons for a more compact and consistent appearance.
Dropdown Behavior	Implement coordinated dropdown state management to ensure only one popup (context, settings, or model selector) is open at a time, fixing the issue where multiple dropdowns could be open simultaneously.
Component Updates	Refactor AgentModelSelector, PromptContextPopup, and PromptSettingsPopup components to support controlled open/close state with toggle and close callbacks.
CSS Adjustments	Update CSS for buttons, icons, and mode indicators to smaller dimensions and tighter spacing.

These changes improve the prompt box usability and visual consistency, especially in narrow sidebar layouts, and prevent overlapping dropdowns for a cleaner user experience.

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