Improve streaming indicators and file attachments during agent actions

What's New

This release addresses several bugs and introduces improvements related to real-time message streaming, specifically for messages containing file attachments.

• Live File Attachments: File attachments (images, videos, audio, etc.) now appear in the UI as the message is streaming, providing immediate feedback to the user.
• More Accurate Streaming Indicator: The logic for displaying the "streaming" animation has been simplified and made more reliable, directly tied to the backend job status. This prevents the indicator from getting stuck or disappearing prematurely.
• Improved Message Visibility: The rules for hiding messages have been refined. Short, operational messages from the agent (like READ actions) will no longer be hidden when they are complete, giving the user better insight into the agent's process.
• Robust Streaming State: The overall management of the streaming state has been improved by using a dedicated store (useStreamingMessagesStore), making the UI more stable and less prone to race conditions.

Impact

• No Breaking Changes: These changes are non-breaking and focus on improving existing functionality.
• Enhanced User Experience: The live display of attachments and more accurate streaming indicators significantly improve the real-time interaction experience with the agent.

PRs

• fix: Display file attachments during streaming by @damianvtran in #76

Full Changelog: v0.12.5...v0.12.6