feat(render): rebuild typst render package cph-render (WU-2)

Single entry `display(info, target, parts)` over an ordered parts array, the
frozen contract the generated typst driver calls. Per-kind dispatch for
segment/example/lemma/sop; student/teacher matrix derived internally from
`target` (student hides example solution + lemma proof; teacher shows all).
Content-field values are consumed as already-evaluated content (driver
`include`s them ⇒ module body, ADR-0006), never imported/stringified. Optional
fields (lemma proof, example source) handled gracefully; unknown kind/target
degrade without crashing. Zero @preview deps (CI-robust); CJK + math styled.
Smoke compiles to non-empty student/teacher PDFs.

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

render/src/style.typ

@@ -0,0 +1,85 @@
+// Base document styling: CJK fonts, headings, math, paragraph layout, page.
+//
+// Zero external dependencies. Heading numbering uses builtin `numbering`
+// strings (no @preview/numbly) so the package compiles with no network.
+
+#import "fonts.typ"
+
+/// Apply the base style to a document body. Used as `show: base-style`.
+#let base-style(doc) = {
+  // Language / region drive CJK line-breaking and punctuation.
+  set text(lang: "zh", region: "cn", size: 12pt, font: fonts.serif)
+  set text(cjk-latin-spacing: auto)
+
+  // Heading numbering: 一、 / 1.1 / 1.1.1 — builtin numbering, no deps.
+  set heading(numbering: "一、")
+  show heading: set text(font: fonts.sans)
+
+  // Number display equations.
+  set math.equation(numbering: "(1)")
+
+  set par(
+    first-line-indent: (amount: 2em, all: true),
+    leading: 0.8em,
+    spacing: 1.5em,
+    justify: true,
+  )
+
+  set page(
+    margin: (x: 2.2cm, y: 2.4cm),
+    footer: context align(center)[
+      #counter(page).get().at(0) / #counter(page).final().at(0)
+    ],
+  )
+
+  set table(inset: 5pt, stroke: 0.75pt)
+
+  // Inline quotes -> subtle highlight (matches prototype feel).
+  show quote.where(block: false): it => highlight(
+    it.body,
+    fill: gray.transparentize(60%),
+    top-edge: 1em,
+    bottom-edge: -0.2em,
+    extent: 0.35em,
+    radius: 0.25em,
+  )
+
+  show link: set text(fill: eastern)
+  show link: underline
+
+  doc
+}
+
+/// Cancel the active paragraph first-line indent (for tag lines that should
+/// start flush-left). Defensive against both `length` and `dict` indent forms.
+#let no-indent = context {
+  let fli = par.first-line-indent
+  if type(fli) == length {
+    h(-fli)
+  } else {
+    h(-fli.amount)
+  }
+}
+
+/// Document title block.
+#let title-block() = {
+  set align(center)
+  set text(font: fonts.sans, size: 22pt, weight: "bold")
+  context document.title
+}
+
+/// Subtitle + authors block under the title.
+#let subtitle-block(subtitle) = {
+  set align(center)
+  set text(size: 14pt)
+  v(1.2em, weak: true)
+  subtitle
+  context {
+    let authors = document.author
+    if authors != () {
+      v(0.8em, weak: true)
+      authors.join(h(1.5em))
+    }
+  }
+  v(1.2em, weak: true)
+}