Prepare 1.0.0-beta.25 release notes

[Hameedkunkanoor]

Description

This PR prepares Azure.AI.AgentServer.Core 1.0.0-beta.25 release notes by:

• Finalizing the beta.25 changelog date as 2026-05-23.
• Adding the bug-fix note for telemetry attribute key migration from gen_ai.agent.blueprint.id to microsoft.a365.agent.blueprint.id.

Relevant PRs:

• .NET fix: Fix blueprint_id attribute key to microsoft.a365.agent.blueprint.id #59422
• Python parity reference: Fix blueprint_id attribute key to microsoft.a365.agent.blueprint.id azure-sdk-for-python#47094

No API spec regeneration is included in this PR.

All SDK Contribution checklist:

• The pull request does not introduce breaking changes.
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message.

Testing Guidelines

• Pull request includes test coverage for the included changes.

Testing note:
This is a changelog-only release preparation PR. Functional validation is covered in PR #59422.

[Copilot]

Pull request overview

Prepares the Azure.AI.AgentServer.Core 1.0.0-beta.25 release notes by finalizing the release date and documenting a telemetry tag key migration for blueprint ID to align with the Agent365/A365 schema.

Changes:

• Set 1.0.0-beta.25 CHANGELOG header from “Unreleased” to the release date 2026-05-23.
• Added a “Bugs Fixed” entry describing the blueprint telemetry attribute key change from gen_ai.agent.blueprint.id to microsoft.a365.agent.blueprint.id.