feat(checker): cph-model — structured export-target build config (WU-B, ADR-0009)

manifest.toml [targets.*] upgraded from bare names to structured build configs.
Lesson.targets: Vec<String> → Vec<TargetConfig> { name, artifact, numbering }.
ArtifactKind { SingleFile, FileTree } mirrors Spec.Courseware.Artifact.
NumberingConfig.heading: Option<Vec<String>> — None means "use framework
default" (render package owns it), so absence is distinguishable from a value.
Empty [targets.x] body = all defaults, no diagnostics. Malformed config (bad
artifact value, non-array numbering.heading) → non-fatal SchemaViolation, target
kept with defaults. Enabled toml `preserve_order` so target declaration order is
real (the old Vec<String> never actually preserved order). target_names() helper
for call sites that only want names. 8 tests green.

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

crates/cph-model/tests/fixtures/bad-target-config/manifest.toml

@@ -0,0 +1,16 @@
+[project]
+id = "fixture-bad-target-config"
+name = "bad-target-config"
+
+[info]
+title = "测试课：非法导出目标配置"
+
+# Invalid artifact value → SchemaViolation, falls back to default (single-file).
+[targets.student]
+artifact = "pdf-thing"
+
+# numbering.heading is not an array of strings → SchemaViolation, heading None.
+[targets.teacher]
+artifact = "file-tree"
+[targets.teacher.numbering]
+heading = "not-an-array"

crates/cph-model/tests/fixtures/target-configs/manifest.toml

@@ -0,0 +1,19 @@
+[project]
+id = "fixture-target-configs"
+name = "target-configs"
+
+[info]
+title = "测试课：导出目标的结构化 build 配置"
+
+# Full config: explicit artifact + numbering.heading override.
+[targets.student]
+artifact = "single-file"
+[targets.student.numbering]
+heading = ["{1:一}、", "{1:1}.{2:1}", "{1:1}.{2:1}.{3:1}"]
+
+# file-tree artifact, no presentation override.
+[targets.archive]
+artifact = "file-tree"
+
+# Empty body → all defaults.
+[targets.teacher]