…undry Annotations (microsoft#12152)

### Motivation and Context

When invoking an Azure AI Foundry agent via AzureAIAgent, url_citation
metadata such as the document filename (title) is omitted in the
resulting AnnotationContent. Only the url field is populated; the
filename (title) is lost, and no structured metadata is retained. This
breaks traceability and rich citation in downstream responses.

This PR updates the annotation mapping to include the title from
url_citation into the resulting AnnotationContent.

This PR also updates the content types to properly show the present
information either in the `to_dict()` call or `to_str` call, as well as
handling the attributes for the `from_element` class method.

<!-- Thank you for your contribution to the semantic-kernel repo!
Please help reviewers and future users, providing the following
information:
  1. Why is this change required?
  2. What problem does it solve?
  3. What scenario does it contribute to?
  4. If it fixes an open issue, please link to the issue here.
-->

### Description

Citations in responses returned via AzureAIAgent now retain the full
provenance information (url, title, etc.) as delivered by the underlying
agent, matching the behavior observed with direct AIProjectClient calls.
- Closes microsoft#12133 
- Adds further unit tests to validate functionality

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [X] I didn't break anyone 😄