Update README to clarify DTFx as a legacy library

[Tomer Rosenthal (torosent)]

This pull request updates the README.md to clarify the support status of the Durable Task Framework (DTFx) and guide users toward modern, supported alternatives. It also improves documentation clarity around legacy components and removes outdated references.

Key documentation and guidance updates:

Deprecation and support status:

• Added a prominent notice that DTFx is a legacy library, not officially supported by Microsoft, and recommended alternatives such as Durable Functions and Durable Task SDKs with the Durable Task Scheduler backend.

Clarifications and documentation improvements:

• Updated the documentation section to indicate that the docs are legacy and no longer maintained.
• Added a note clarifying that DurableTask.Emulator is a legacy in-memory backend for DTFx and is not the same as the supported Durable Task Scheduler emulator.
• Removed references to the unmaintained GitHub wiki to prevent confusion. [1][2]

[Copilot]

Pull request overview

Updates the root README to clearly communicate that Durable Task Framework (DTFx) is a legacy library and to guide users toward supported Microsoft orchestration alternatives.

Changes:

• Adds a prominent legacy/unsupported notice with links to Durable Functions and Durable Task Scheduler-based SDKs.
• Updates the introductory DTFx description to reflect legacy status and self-management requirements.
• Removes the “under active development” claim for DurableTask.Core and clarifies emulator naming/positioning.

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[Copilot]

Pull request overview

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