feat(cph): implement nested outline manifest and batch/combined export

ADR-0029 — nested outline manifest, supersedes ADR-0008's flat [[parts]]:
- cph-model: recursive loader over manifest.toml containers / element.toml
  leaves; Lesson.parts (pure elements, DFS order) + Lesson.outline (elements
  interleaved with section headings at their DFS-open position); rejects
  ambiguous/incomplete folders and root-vs-container table misplacement
- cph-diag: new DiagCode::ManifestMalformed for carrier-document structure
  errors (discharges an existing TODO)
- cph-typst: augmented manifest now serializes the outline (element/section
  entries) instead of a flat parts array
- render/lib.typ: render-lesson renders section headings at their depth
- examples/TH-141 migrated to 5 nested section containers + 3 root segments,
  byte-identical element order; smoke-verified via cph check/build + pdftotext

ADR-0030 — batch & combined export, extends ADR-0009/0011:
- cph build with no --target batches every declared target (repeatable
  --target for an explicit subset); any target failure => non-zero exit,
  per-target ledger, independent per-target execution
- cph-model: bundle.toml loader (directory + [info]/[targets.*]/ordered
  lessons with per-lesson target overrides)
- cph-typst: augmented bundle manifest (path-prefixed member outlines),
  Engine::{compile_check_bundle,build_bundle_pdf}
- render/lib.typ: render-bundle assembles member lessons under per-lesson
  headings, depth-shifts their own section headings, resets example/lemma
  counters at each lesson boundary by default
- cph-cli: `cph bundle <path> --target <name>` subcommand, same batching
  contract as `cph build`
- new bundle fixtures/tests (cph-model unit + cph-typst through-template PDF
  compile), smoke-verified via a real 2-lesson merged PDF

Verification: cargo fmt/clippy/test clean across the workspace (68 tests);
real cph check/build/bundle runs against TH-141 and a bundle fixture, PDF
content inspected via pdftotext.

render/examples/smoke-eng/exports/teacher.typ

@@ -1,4 +1,4 @@
-// DEFAULT TEACHER TEMPLATE (framework default; ADR-0011).
+// DEFAULT TEACHER TEMPLATE (framework default; ADR-0011, outline shape ADR-0029).
 //
 // Lives in an engineering file at `exports/teacher.typ`. Compiled AS MAIN with
 // the manifest injected:
@@ -18,38 +18,47 @@
 // Read the injected manifest (a path string relative to typst --root).
 #let manifest = toml(sys.inputs.manifest)
 #let info = manifest.at("info", default: (:))
-#let raw-parts = manifest.at("parts", default: ())
+#let raw-outline = manifest.at("outline", default: ())
 
-// Assemble each part: include its content fields (computed absolute paths,
-// resolved against --root) and read scalar fields from <path>/element.toml.
-// `part-fields` (from cph-render) is the single source of truth for kind->fields.
-#let parts = raw-parts.map(raw => {
-  let kind = raw.at("kind", default: none)
-  let path = raw.at("path", default: none)
-  let spec = part-fields.at(kind, default: (content: (), optional-content: (), scalars: ()))
-  // Which optional content fields are present on disk (manifest-declared).
-  let present = raw.at("fields", default: ())
-  let part = (kind: kind)
+// Assemble each outline entry: an "element" entry includes its content fields
+// and reads scalars from element.toml; a "section" entry (ADR-0029) passes
+// title/depth straight through as a heading, no content to load.
+#let outline = raw-outline.map(raw => {
+  if raw.at("type", default: "element") == "section" {
+    (
+      entry-type: "section",
+      kind: raw.at("kind", default: none),
+      title: raw.at("title", default: ""),
+      depth: raw.at("depth", default: 1),
+    )
+  } else {
+    let kind = raw.at("kind", default: none)
+    let path = raw.at("path", default: none)
+    let spec = part-fields.at(kind, default: (content: (), optional-content: (), scalars: ()))
+    // Which optional content fields are present on disk (manifest-declared).
+    let present = raw.at("fields", default: ())
+    let entry = (entry-type: "element", kind: kind)
 
-  // Required content fields: <path>/<field>.typ (absolute, root-relative).
-  for field in spec.content {
-    part.insert(field, include "/" + path + "/" + field + ".typ")
-  }
-  // Optional content fields: only when the manifest says the file exists.
-  for field in spec.optional-content {
-    if field in present {
-      part.insert(field, include "/" + path + "/" + field + ".typ")
+    // Required content fields: <path>/<field>.typ (absolute, root-relative).
+    for field in spec.content {
+      entry.insert(field, include "/" + path + "/" + field + ".typ")
     }
-  }
-  // Scalar fields come from <path>/element.toml.
-  if spec.scalars.len() > 0 {
-    let element = toml("/" + path + "/element.toml")
-    for field in spec.scalars {
-      let v = element.at(field, default: none)
-      if v != none and v != "" { part.insert(field, v) }
+    // Optional content fields: only when the manifest says the file exists.
+    for field in spec.optional-content {
+      if field in present {
+        entry.insert(field, include "/" + path + "/" + field + ".typ")
+      }
     }
+    // Scalar fields come from <path>/element.toml.
+    if spec.scalars.len() > 0 {
+      let element = toml("/" + path + "/element.toml")
+      for field in spec.scalars {
+        let v = element.at(field, default: none)
+        if v != none and v != "" { entry.insert(field, v) }
+      }
+    }
+    entry
   }
-  part
 })
 
 // Presentation: per-level heading numbering. Default (一、 / 1.1 / 1.1.1) comes
@@ -57,6 +66,6 @@
 #render-lesson(
   info: info,
   target: target,
-  parts: parts,
+  outline: outline,
   heading-numbering: default-heading-numbering,
 )