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/typst.toml

@@ -6,3 +6,13 @@ compiler = "0.15.0"
 authors = ["curriculum-project-hub"]
 license = "MIT"
 description = "Curriculum lesson render package: single `display` entry over an ordered list of typed parts (segment/example/lemma/sop), targeting student/teacher handouts."
+
+# External @preview dependencies (resolved via the typst package registry):
+#   @preview/numbly:0.1.0  — per-level heading numbering (src/style.typ).
+# numbly is dependency-free (pure typst). For network-free CI the package is
+# VENDORED in-repo at:
+#   render/vendor/typst-packages/preview/numbly/0.1.0/
+# mirroring the typst preview-cache layout
+# ({cache}/typst/packages/preview/numbly/0.1.0/). Point typst's package cache /
+# resolver at render/vendor/typst-packages (e.g. TYPST_PACKAGE_CACHE_PATH or the
+# embedded World's preview dir) so `@preview/numbly:0.1.0` resolves offline.