feat(render): rebuild typst render package cph-render (WU-2)

Single entry `display(info, target, parts)` over an ordered parts array, the
frozen contract the generated typst driver calls. Per-kind dispatch for
segment/example/lemma/sop; student/teacher matrix derived internally from
`target` (student hides example solution + lemma proof; teacher shows all).
Content-field values are consumed as already-evaluated content (driver
`include`s them ⇒ module body, ADR-0006), never imported/stringified. Optional
fields (lemma proof, example source) handled gracefully; unknown kind/target
degrade without crashing. Zero @preview deps (CI-robust); CJK + math styled.
Smoke compiles to non-empty student/teacher PDFs.

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

render/examples/smoke-parts.typ

@@ -0,0 +1,70 @@
+// Shared hand-written sample lesson exercising all 4 kinds.
+// Content field values are plain content blocks — exactly what the Rust driver
+// would hand us via `include`.
+
+#let info = (
+  title: "向量与几何 · 示例讲义",
+  author: ("张老师", "李老师"),
+)
+
+#let parts = (
+  // segment
+  (
+    kind: "segment",
+    textbook: [
+      本节研究平面向量的基本运算。设 $arrow(a)$、$arrow(b)$ 为平面内两个向量，
+      其数量积定义为 $arrow(a) dot arrow(b) = |arrow(a)| |arrow(b)| cos theta$，
+      其中 $theta$ 为两向量的夹角。
+    ],
+  ),
+  // example WITH source
+  (
+    kind: "example",
+    source: "2024 高考甲卷",
+    problem: [
+      已知 $arrow(a) = (1, 2)$，$arrow(b) = (3, -1)$，求 $arrow(a) dot arrow(b)$。
+    ],
+    solution: [
+      由坐标公式，$arrow(a) dot arrow(b) = 1 times 3 + 2 times (-1) = 3 - 2 = 1$。
+    ],
+  ),
+  // example WITHOUT source
+  (
+    kind: "example",
+    problem: [
+      求向量 $arrow(a) = (3, 4)$ 的模长 $|arrow(a)|$。
+    ],
+    solution: [
+      $|arrow(a)| = sqrt(3^2 + 4^2) = sqrt(25) = 5$。
+    ],
+  ),
+  // lemma WITH proof
+  (
+    kind: "lemma",
+    stmt: [
+      对任意向量 $arrow(a)$、$arrow(b)$，有 $|arrow(a) dot arrow(b)| <= |arrow(a)| |arrow(b)|$。
+    ],
+    proof: [
+      由数量积定义 $arrow(a) dot arrow(b) = |arrow(a)| |arrow(b)| cos theta$，
+      又 $|cos theta| <= 1$，故 $|arrow(a) dot arrow(b)| = |arrow(a)| |arrow(b)| |cos theta| <= |arrow(a)| |arrow(b)|$。
+      $qed$
+    ],
+  ),
+  // lemma WITHOUT proof (proof key omitted entirely)
+  (
+    kind: "lemma",
+    stmt: [
+      两个非零向量垂直当且仅当其数量积为零，即 $arrow(a) perp arrow(b) <==> arrow(a) dot arrow(b) = 0$。
+    ],
+  ),
+  // sop
+  (
+    kind: "sop",
+    sop: [
+      求两向量夹角的标准步骤：
+      + 计算数量积 $arrow(a) dot arrow(b)$；
+      + 分别计算模长 $|arrow(a)|$、$|arrow(b)|$；
+      + 代入 $cos theta = (arrow(a) dot arrow(b)) / (|arrow(a)| |arrow(b)|)$ 求出 $theta$。
+    ],
+  ),
+)