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/manifest.toml

@@ -1,11 +1,15 @@
-# Throwaway smoke engineering file for the cph-render template round (ADR-0011).
-# Exercises all 4 kinds + nested headings (per-level numbering) + an example with
-# a `source` scalar and one without + a lemma with proof and one without.
+# Throwaway smoke engineering file for the cph-render template round
+# (ADR-0011, outline shape ADR-0029). Exercises all 4 kinds + a section heading
+# + nested headings (per-level numbering) + an example with a `source` scalar
+# and one without + a lemma with proof and one without.
 #
-# The per-part `fields` array lists the content fields present ON DISK. The
-# template uses it to decide whether to load OPTIONAL content (lemma `proof`),
-# because typst has no file-exists primitive. (OPEN: the exact manifest shape for
-# declaring optional-field presence is for the Rust/manifest contract to pin.)
+# This file is compiled DIRECTLY via `typst compile --input manifest=/manifest.toml`
+# (see README below), bypassing the Rust engine's augmented-manifest builder
+# (`cph_typst::build_augmented_manifest`). So the `[[outline]]` shape here is
+# hand-authored to already be what that builder would produce: an ordered array
+# of `type = "element"` (kind, path, fields — the content fields present on
+# disk, since typst has no file-exists primitive) and `type = "section"`
+# (kind, title, depth) entries.
 
 [project]
 id   = "smoke-eng"
@@ -15,38 +19,54 @@ name = "cph-render template smoke"
 title  = "向量与几何 · 示例讲义"
 author = ["张老师", "李老师"]
 
-# segment — nested headings exercise per-level numbering (一、 / 1.1 / 1.1.1).
-[[parts]]
+# segment — exercises per-level numbering (一、 / 1.1 / 1.1.1) alongside the
+# section heading below.
+[[outline]]
+type   = "element"
 kind   = "segment"
 path   = "segments/向量数量积"
 fields = ["textbook"]
 
+# A section heading (ADR-0029): opens depth-1, groups the two examples that
+# follow. Contributes no element to the sequence.
+[[outline]]
+type  = "section"
+kind  = "section"
+title = "数量积的坐标计算"
+depth = 1
+path  = "examples"
+
 # example WITH source scalar
-[[parts]]
+[[outline]]
+type   = "element"
 kind   = "example"
 path   = "examples/坐标数量积"
 fields = ["problem", "solution"]
 
 # example WITHOUT source scalar
-[[parts]]
+[[outline]]
+type   = "element"
 kind   = "example"
 path   = "examples/求模长"
 fields = ["problem", "solution"]
 
 # lemma WITH proof (proof.typ present on disk; declared in fields)
-[[parts]]
+[[outline]]
+type   = "element"
 kind   = "lemma"
 path   = "lemmas/柯西不等式"
 fields = ["stmt", "proof"]
 
 # lemma WITHOUT proof (proof.typ absent; fields omits it)
-[[parts]]
+[[outline]]
+type   = "element"
 kind   = "lemma"
 path   = "lemmas/垂直判据"
 fields = ["stmt"]
 
 # sop
-[[parts]]
+[[outline]]
+type   = "element"
 kind   = "sop"
 path   = "sops/求夹角步骤"
 fields = ["sop"]