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-check/src/lib.rs

@@ -60,6 +60,13 @@ impl CheckReport {
     }
 
     /// Whether any collected diagnostic is `Error`-severity.
+    ///
+    /// **Legality decision (spec alignment).** `!has_errors()` is the
+    /// implementation of `Spec.Courseware.Legal` (`spec/Spec/Courseware/Diagnostic.lean`):
+    /// a lesson is *legal* iff its diagnostics contain no error-level diagnostic
+    /// (warnings are non-blocking — see `Severity` / ADR-0010). There is no CI
+    /// gate enforcing this alignment (repo constitution); it is kept greppable
+    /// here so a reviewer can tie the orchestrator's gate to the Lean master.
     pub fn has_errors(&self) -> bool {
         self.diagnostics
             .iter()
@@ -247,7 +254,7 @@ fn compile_targets(lesson: &cph_model::Lesson) -> Vec<&str> {
     if lesson.targets.is_empty() {
         vec![DEFAULT_TARGET]
     } else {
-        lesson.targets.iter().map(String::as_str).collect()
+        lesson.target_names()
     }
 }
 
@@ -271,11 +278,11 @@ fn render_coverage(lesson: &cph_model::Lesson, known: &[&str]) -> Vec<Diagnostic
             continue;
         }
         for target in &lesson.targets {
-            let covered = COVERED_TARGETS.contains(&target.as_str());
+            let covered = COVERED_TARGETS.contains(&target.name.as_str());
             if covered {
                 continue;
             }
-            let key = (part.kind.clone(), target.clone());
+            let key = (part.kind.clone(), target.name.clone());
             if seen.contains(&key) {
                 continue;
             }
@@ -284,12 +291,12 @@ fn render_coverage(lesson: &cph_model::Lesson, known: &[&str]) -> Vec<Diagnostic
                 DiagCode::RenderIgnored,
                 format!(
                     "kind '{}' has no render rule for target '{}'; it will be omitted from that export",
-                    part.kind, target
+                    part.kind, target.name
                 ),
             )
             .with_hint(format!(
                 "add a render rule for kind '{}' under target '{}', or remove the target",
-                part.kind, target
+                part.kind, target.name
             ));
             // Pin the severity via the named contract const. `Diagnostic::warning`
             // already produces a warning, but assigning the const keeps the