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/lib.typ

@@ -23,7 +23,7 @@
 //             fields). Never crashes. The "no render rule => warning"
 //             diagnostic is the Rust side's job, not ours.
 
-#import "src/style.typ": base-style, title-block, subtitle-block
+#import "src/style.typ": base-style, default-heading-numbering, title-block, subtitle-block
 #import "src/elements/segment.typ": display-segment
 #import "src/elements/example.typ": display-example
 #import "src/elements/lemma.typ": display-lemma
@@ -75,17 +75,34 @@
 /// - `info`:   dict, e.g. (title: "…", author: "…"). `author` may be absent.
 /// - `target`: string. MVP: "student" | "teacher". Unknown => conservative.
 /// - `parts`:  ordered array of part dicts (see file header).
-#let display(info: (:), target: "student", parts: ()) = {
+/// - `config`: dict carrying the target's build/presentation overrides
+///             (ADR-0009). Open/forward-compatible — read keys with
+///             `.at(.., default: ..)`. Recognised keys (MVP):
+///               `config.numbering.heading`: array of per-level numbly pattern
+///                 strings, e.g. `("{1:一}、", "{1:1}.{2:1}")`. Optional; when
+///                 absent the framework default (correct per-level scheme) is
+///                 used. Future presentation knobs slot in without touching
+///                 this signature.
+#let display(info: (:), target: "student", parts: (), config: (:)) = {
   let title = info.at("title", default: [])
   let author = info.at("author", default: none)
 
+  // Resolve presentation config -> framework defaults, file may override.
+  // `config.numbering.heading` (array of numbly patterns) overrides the
+  // framework default per-level numbering when present.
+  let numbering-cfg = config.at("numbering", default: (:))
+  let heading-numbering = numbering-cfg.at(
+    "heading",
+    default: default-heading-numbering,
+  )
+
   // `document` author wants a string/array; normalise the optional field.
   set document(
     title: title,
     author: if author == none { () } else { author },
   )
 
-  show: base-style
+  show: base-style.with(heading-numbering: heading-numbering)
 
   // Reset shared counters so each rendered lesson numbers from 1.
   example-counter.update(0)