feat(spec): Artifact gets fields, target = artifact + typed steps, drop RenderRule (ADR-0011)

Fix the abstraction level review flagged. lake build green (20 jobs), no sorry.

- Artifact.lean: bare enum → ADT with fields — singleFile(filepath) /
  fileTree(root, outputs:glob). The product semantics (one file where, vs a tree
  of what) are pinned in fields + doc, not erased behind empty constructors.
  Paths/globs carried as String (semantics in doc; no filesystem algebra).
- Render.lean: Step inductive (typstCompile(template) | shell(run)) replaces the
  loose BuildStepForm. TargetSpec = artifact + steps:List Step + covers:Kind→Prop
  (the old renders:Kind→Option RenderRule is gone — coverage is now a plain
  declaration; the render "how" lives in the typstCompile template). covers /
  renderIgnored semantics continuous with ADR-0005.
- Primitives.lean: RenderRule field removed (the per-target payload is retired per
  ADR-0011); a note records where the "how" now lives.
- Diagnostic.lean unchanged in meaning (covers signature stable; Legal still
  quantifies over declared targets).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

spec/Spec/Courseware/Primitives.lean

@@ -40,15 +40,11 @@ structure Primitives where
   "存在一个由 kind 决定的合法数据类型",不复刻 JSON Schema / typst Content 的形状。
   -/
   ElementData : KindId → Type
-  /-- export target 的标识(`PINNED` 角色, ADR-0005;表示 `OPEN`)。一个 target 是对 lesson 的一种投影(讲义/教案/PPT/平台 archive…)。 -/
+  /-- export target 的标识(`PINNED` 角色, ADR-0005;表示 `OPEN`)。一个 target 是一次 build,产出对 lesson 的一种投影(讲义/教案/PPT/平台 archive…),见 `Render`。 -/
   TargetId : Type
-  /--
-  渲染规则的载荷(表示 `OPEN`, ADR-0005)。
 
-  "某 kind 在某 target 下如何呈现"那条规则的**内容**。typst 是渲染后端之一(`PINNED`,
-  ADR-0005)、不是定义语言;但渲染管线/规则载荷的具体表示仍 `OPEN`。契约只关心规则
-  **在不在**(见 `Render`),不碰它是什么。
-  -/
-  RenderRule : Type
+-- 注:原有 `RenderRule : Type` 已随 ADR-0011 移除。渲染的"how"不再是契约层的 per-target
+-- 载荷,而是 `Render.TargetSpec.steps` 里 `typstCompile` step 所引用的**模板文件**承载;
+-- 契约只保留覆盖声明 `TargetSpec.covers`(该 target 渲染哪些 kind),供种子诊断用。
 
 end Spec.Courseware