docs(developers): add missing Task Dispatch section and diagram to protocol.md (EN)

[princexpoddar]

What is missing or unclear:

In the EN version of docs/developers/protocol.md only covers the first half of the protocol lifecycle: Device Registration...It is completely missing the second half: Task Dispatch / Scheduling Decisions.

The Chinese documentation (i18n/zh/.../developers/protocol.md) already contains this explanation and references the architectural diagram static/img/docs/common/developers/protocol/task-dispatch.png. The image asset already exists in the repository, and this EN/ZH discrepancy was also noted in docs/diagrams-inventory.md (lines 244–250).

Where it should go (existing page, or a new page):

Existing page:

• docs/developers/protocol.md (under a new section ## Task Dispatch & Scheduling Decisions)
• Synced to versioned_docs/version-v2.9.0/developers/protocol.md

Why this would help:

1. Developer Parity: Brings the English documentation to parity with the Chinese docs.
2. Architecture Clarity: Provides developers and contributors with a complete, end-to-end picture of how the scheduler and device-plugin coordinate GPU slicing without having to trace through the Go source code.
3. Resolves Known Audit Gap: Closes the documented diagram/content inconsistency listed in docs/diagrams-inventory.md.