Phase 3: generate target repo issue template (.github/ISSUE_TEMPLATE/agent-work-item.md) as part of directed context output

[TGPSKI]

Context

• SKILL.md (generate-directed-contexts)
• references/phase-03-generate.md (definition of Phase 3 generation steps, currently has Steps 1-6)
• The agent-work-item.md issue template was added to the directed-contexts repo itself in a prior pass; now the skill generator must output it when generating for any target repo.

Work

• Add a new Step 7 to the Phase 3 generation pipeline (between Step 6 route-case fixtures and the PR Checkpoint) that generates an .github/ISSUE_TEMPLATE/agent-work-item.md for the target repo:

  ---
  name: Agent work item
  about: Minimal issue body for agent-consumable units of work
  title: ""
  labels: agent-work
  ---
  
  ## Context
  - AGENTS.md
  
  ## Work
  - [ ] 

  The template body is a skeleton with one unchecked checkbox for Work items.

• Wire into the Phase 3 generation so the Context line references the repo-primary instruction file detected in Phase 1 (scan output carries instruction_surfaces; the first/shortest surface path is the primary — e.g. AGENTS.md for most repos, SKILL.md for skill repos). The generated template inserts this path dynamically.

• Update the PR Checkpoint in Phase 3 (references/phase-03-generate.md line ~127) to list .github/ISSUE_TEMPLATE/agent-work-item.md in the "Files to include" block.

• Update the Phase 2 boundary model output to include this new generated file in the proposal table so the user sees it before confirming writes.

• Update references/phase-04-validate.md golden examples to verify the template exists and the Context line matches the repo's primary instruction file (detected in Phase 1).

• Check the existing examples (examples/abductive-triage/, examples/security-context-spec/) — if either expected/ AGENTS.md references an issue template, note that the template now gets auto-generated rather than hand-authored.