feat(checker): align cph-typst + cph-check to export-as-build model (WU-D)

Integrate the WU-B (structured targets) and WU-C (numbly, config) changes.

cph-typst:
- World resolves any @preview/* package from the in-repo vendored dir
  (<render_dir>/vendor/typst-packages/preview/<name>/<version>/), fully offline —
  no typst-kit download. Proven: build_pdf_with_real_render compiles the real
  render package (which imports @preview/numbly:0.1.0) through the embedded
  engine, PDF out.
- Driver threads each target's presentation config: looks up the TargetConfig by
  name, emits `config: (numbering: (heading: (...)))` (escaped) when an override
  is present, else `config: (:)` (render default).
- target_precheck guards artifact/target: FileTree → blocking diagnostic (MVP is
  single-file, deferred per ADR-0009); --target not declared → blocking
  diagnostic; no-targets lesson still defaults through.

cph-check:
- Migrated to Lesson.targets: Vec<TargetConfig> (target_names() / target.name at
  the 6 sites). Pipeline unchanged (already matches ADR-0010 phases). Documented
  that !has_errors() implements Spec.Courseware.Legal (no error-level diagnostic).

Workspace: fmt + clippy -D warnings + all tests green.

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

crates/cph-typst/tests/compile.rs

@@ -78,6 +78,53 @@ fn optional_proof_included_when_present() {
     assert!(src.contains("_p1_proof = include"));
 }
 
+/// The mini fixture's targets carry no `numbering.heading` override, so the
+/// driver emits an empty `config: (:)` (render package applies its default).
+#[test]
+fn driver_emits_empty_config_when_no_override() {
+    let lesson = load_mini();
+    let src = generate_driver(&lesson, "student");
+    assert!(
+        src.contains("config: (:)"),
+        "expected empty config for a target with no numbering override:\n{src}"
+    );
+}
+
+/// CONFIG THREADING: a target declaring a `numbering.heading` override produces
+/// a driver that passes `config: (numbering: (heading: (...)))` with the
+/// patterns as escaped typst string literals, in order.
+#[test]
+fn driver_threads_numbering_heading_config() {
+    use cph_model::{ArtifactKind, Info, Lesson, NumberingConfig, Project, TargetConfig};
+    use std::path::PathBuf;
+
+    let lesson = Lesson {
+        project: Project {
+            id: "x".into(),
+            name: "x".into(),
+        },
+        info: Info {
+            title: "t".into(),
+            author: None,
+        },
+        parts: vec![],
+        targets: vec![TargetConfig {
+            name: "student".into(),
+            artifact: ArtifactKind::SingleFile,
+            numbering: Some(NumberingConfig {
+                heading: Some(vec!["{1:一}、".into(), "{1:1}.{2:1}".into()]),
+            }),
+        }],
+        root: PathBuf::from("/tmp/does-not-matter"),
+    };
+
+    let src = generate_driver(&lesson, "student");
+    assert!(
+        src.contains(r#"config: (numbering: (heading: ("{1:一}、", "{1:1}.{2:1}",)))"#),
+        "expected threaded numbering config in driver:\n{src}"
+    );
+}
+
 /// FONT-DEPENDENT: compile the mini lesson through the render-stub. Should
 /// produce zero Error-severity diagnostics. If this fails purely because the
 /// test host lacks fonts, the failure will be a typst font error — see the
@@ -166,6 +213,13 @@ fn driver_internal_span_is_repointed() {
 /// targets. This proves the whole World → driver → render-package → PDF path,
 /// not just the stub. Requires system CJK fonts (present on dev + CI via
 /// fonts-noto-cjk).
+///
+/// **This is also the offline-`@preview/numbly` proof (Task 1).** The real
+/// render package's `src/style.typ` does `#import "@preview/numbly:0.1.0"`, so a
+/// clean PDF here means the embedded `World` resolved numbly from the vendored
+/// dir (`render/vendor/typst-packages/preview/numbly/0.1.0/`) with no network /
+/// package download — had it failed, `build_pdf` would have returned a
+/// package-not-found error and this test would panic.
 #[test]
 fn build_pdf_with_real_render() {
     let lesson = load_mini();
@@ -175,6 +229,14 @@ fn build_pdf_with_real_render() {
         "real render package missing at {}",
         render_dir.display()
     );
+    // Sanity: the numbly the render package imports is actually vendored here.
+    assert!(
+        render_dir
+            .join("vendor/typst-packages/preview/numbly/0.1.0/lib.typ")
+            .is_file(),
+        "vendored numbly missing under {}",
+        render_dir.display()
+    );
     let engine = Engine::with_render_dir(render_dir);
 
     for target in ["student", "teacher"] {
@@ -183,6 +245,10 @@ fn build_pdf_with_real_render() {
             .unwrap_or_else(|d| panic!("{target} PDF build failed: {d:#?}"));
         assert!(pdf.starts_with(b"%PDF"));
         assert!(pdf.len() > 1024, "{target} PDF too small");
+        eprintln!(
+            "build_pdf_with_real_render: {target} PDF = {} bytes (numbly resolved offline)",
+            pdf.len()
+        );
         let out = std::env::temp_dir().join(format!("cph-typst-mini-real-{target}.pdf"));
         std::fs::write(&out, &pdf).expect("write pdf");
     }