Chore: Align Status Icons in agent_status_icon component

What does this MR do and why?

This MR updates the agent-status-icon component and related badge components to use the updated standard (across the board) use of icons for sessions.

References

• Related GitLab Work Item: #629573 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

For DAP/General Setup

• General DAP: https://docs.gitlab.com/development/duo_agent_platform/
• Assigning Duo to a group: https://docs.gitlab.com/development/ai_features/#run-gitlabduosetup-script
• Make sure you are in SaaS mode with export GITLAB_SIMULATE_SAAS=1 set in your env.runit file in your local gdk.
• Make sure you have docker and gitlab runners up.

Adding Sessions

1. A: If you see no Sessions, you can trigger one that displays a Pipeline/Job by going to an Issue within your Duo enabled project and clicking the Generate MR with Duo button. It should trigger a new session that you can open up.
2. B: You can also run the following query bundle exec rake "gitlab:duo_workflow:populate[50,20,1,<<YOUR_TEST_GROUP_PATH_HERE>>]" to create new agent sessions. Refresh the page. Make sure the group you are testing in has Duo assigned (see DAP setup above).

The actual testing

Test Work Item or Merge Request Session Widget

1. Generate a new Session from a Work Item or Merge Request. You can do this by either doing a comment (@duo developer for example) or using Plan (at the top right of Work Items only).
2. Notice the Session List Widget has icons laid out appropriately.

Test Sessions on Issue board

1. Go to the Issue board.
2. If you have done one of the above tests with the Session Widget from a Work Item, you should see the Session badge on the work item.
3. Click it.
4. Validate icon(s) appear as expected.

Test Sessions in Chat

0. Make sure docker and gitlab runner are up.
1. Go to the Agentic Chat in the Side Panel on the right.
2. Start a session in chat. An easy way is to be on a Work Item and say: could you use the developer flow to implement this Work Item?. This should start a Session.
3. When a Session starts, validate the icons appear as expected.

Test Sessions List & Session Details

1. Go to AI and select Sessions from the left navigation rail.
2. Validate icons in the Session list appear as expected.
3. Click any Session.
4. Validate in the status badge that the icon within it appears as expected.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #629573 (closed)