Reorder aria label for agent sessions to announce label before type

[Copilot]

Agent session aria labels announced session type before label, violating accessibility best practices of prioritizing critical information.

Changes

• AgentSessionsAccessibilityProvider: Reordered localization parameters in getAriaLabel() to place element.label before element.providerLabel

  • Before: "Background session Explain this screenshot (Completed), created..."
  • After: "Explain this screenshot Background session (Completed), created..."

• Test coverage: Added agentSessionsAccessibilityProvider.test.ts with assertions verifying label precedence in aria output

Original prompt

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This section details on the original issue you should resolve

<issue_title>Aria label of session entries should have type of session at the end</issue_title>
<issue_description>Right now the aria label seems to be TYPE LABEL. Instead it should be LABEL TYPE.
The practice we should follow is to always first announce the most important information to the user, and that is the label of the chat session

@joshspicer @meganrogge </issue_description>

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

• Fixes Aria label of session entries should have type of session at the end #286374

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