Contributors capture ready-to-implement work with a definition of done

User story

As a contributor, I want a work-item issue form for planned, ready-to-implement work so that the change ships with a clear definition of done instead of a free-form description that leaves scope and completion ambiguous.

Why

The bug-report (#407) and feature-request (#408) forms cover reports and requests, but not the third shape the dungeon-studio issue set uses: planned development work broken down for implementation. A work-item form rounds out the set so tracked work carries motivation, concrete scope, and measurable acceptance criteria up front.

Acceptance criteria

• .github/ISSUE_TEMPLATE/work-item.yml exists as a GitHub Issue Form with fields:
  • Title guidance: write the title as a statement that is true when the issue is done (helper text).
  • Summary (multi-line, required).
  • Motivation (multi-line, required).
  • Scope (multi-line, required), placeholder referencing zfs package paths.
  • Acceptance criteria (multi-line, required), task-list syntax, defaulting to - [ ] Tests and pre-commit pass.
  • Additional context (multi-line, optional).
• Form auto-applies the enhancement label.
• Follows the same house style as the sibling forms: no SPDX header, folded scalars, active-voice field descriptions.

Out of scope

• Bug reports and feature requests (tracked by #407 and #408).
• Flipping blank_issues_enabled; that rides with the bug form (#407).

Notes

• Target release: none — chore
• Source: modernization assessment §4, §5 (dungeon-studio issue-form comparison).