[EngSys] Agentic Workflow tweaks (Azure#57793)

* [EngSys] Agentic Workflow tweaks

The focus of these changes is to tune behavior of
the issue triage and samples/docs workflows, to
remove friction and enhance functionality.

Issue Triage:
  - If labeling was successful and a package was
    identified, validate on NuGet that the package
    is not deprecated. If it is, inform the issue
    author and resolve the issue.

Samples and Docs:
  - Revise the workflow to open an issue with a
    detailed set of instructions for a coding agent
    to execute.  Previously, the workflow would
    attempt to create a PR directly, which is blocked
    by Microsoft security policies.  Each run failed
    and produced an issue with a helpful "create PR"
    link but could not be customized and broke
    issue triage requiring frequent manual intervention.

* Address PR review feedback for agentic workflows

- Fix dangling 'Conventions below' reference in docs workflow
- Fix package ID ambiguity in deprecation check (check issue body first, directory fallback, skip if ambiguous)
- Add NuGet registration pagination awareness
- Fix 'no longer published' wording to 'no longer supported'
- Strengthen snippet instructions in Implementation Guide (full lifecycle, #if !SNIPPET, expanded validation)
- Renumber deprecation lookup steps after pagination insertion

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jsquire