fix(templates): help-this-project missing Workflow: Agent Donation marker in body

[castrojo]

Problem

The help-this-project.yml template does not embed Workflow: Agent Donation in the issue body. The lifecycle action detects this marker via grep -Fq "$DONATION_WORKFLOW_MARKER" — without it the donation fast-track is silently skipped and the issue lands in standard triage.

Fix

Add a hidden textarea with the marker as a pre-filled value::

  - type: textarea
    id: workflow-marker
    attributes:
      label: "Workflow"
      value: "Workflow: Agent Donation"
    validations:
      required: true

The marker just needs to survive into the submitted issue body.

Impact

Every issue filed via help-this-project goes through standard triage instead of the donation fast-track. The template's core purpose is broken.