fix(render): per-level heading numbering via numbly; config-driven, offline (WU-C)

Fixes the numbering bug (single pattern "一、" reused across levels → level-2
rendered "二、一、…"). display now takes a `config` dict; heading numbering uses
numbly per level — framework default ("{1:一}、","{1:1}.{2:1}","{1:1}.{2:1}.{3:1}")
→ 一、 / 1.1 / 1.1.1 — overridable via config.numbering.heading from the
engineering file (ADR-0009's file-resident override path, the layer whose absence
caused the bug). Verified: grep "二、一" = 0 across all smoke PDFs.

Adds @preview/numbly:0.1.0 (pure typst, zero transitive deps), VENDORED in-repo
at render/vendor/typst-packages/preview/numbly/0.1.0/ for network-free CI;
resolve via --package-cache-path render/vendor/typst-packages. parts contract +
student/teacher field visibility unchanged.

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

render/examples/smoke-config.typ

@@ -0,0 +1,14 @@
+// Smoke test — exercises the per-target presentation `config` override path
+// (ADR-0009). Here the engineering-file-supplied `config.numbering.heading`
+// overrides the framework-default heading numbering. The patterns happen to
+// match the correct per-level scheme (level-1 `一、`, level-2 `1.1`), proving
+// the override is wired AND yields correct (NOT `二、一、`) output.
+#import "../lib.typ": display
+#import "smoke-parts.typ": info, parts
+
+#display(
+  info: info,
+  target: "teacher",
+  parts: parts,
+  config: (numbering: (heading: ("{1:一}、", "{1:1}.{2:1}"))),
+)

render/examples/smoke-parts.typ

@@ -8,13 +8,26 @@
 )
 
 #let parts = (
-  // segment
+  // segment — with NESTED headings so per-level numbering is visible:
+  //   level-1 `=` should render `一、`, level-2 `==` should render `1.1`
+  //   (NOT the old buggy `二、一、`).
   (
     kind: "segment",
     textbook: [
+      = 平面向量的数量积
+
       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。
+
+      == 坐标表示
+
+      在直角坐标系下，若 $arrow(a) = (x_1, y_1)$、$arrow(b) = (x_2, y_2)$，则
+      $arrow(a) dot arrow(b) = x_1 x_2 + y_1 y_2$。
+
+      == 几何意义
+
+      数量积等于一个向量的模与另一向量在其方向上投影之积。
     ],
   ),
   // example WITH source