fix(typst): ship template as partials so code blocks render (#12)

The single-file `template: civilytics-typst.typ` discarded Quarto's
auto-generated `definitions` partial, so any Typst document containing a
code block failed with `unknown variable: Skylighting`.

Ship the template as Quarto template-partials instead, so Quarto keeps its
definitions (Skylighting + token functions) and syntax-highlighted code
blocks render while the Civilytics branding still applies:

- split civilytics-typst.typ into typst-template.typ (the styling function)
  and typst-show.typ (the show/entry point, keyword-safe [ ] wrapping kept);
  remove the single-file template
- use_civilytics_theme() now copies both partials and prints the
  template-partials usage
- example report.qmd uses template-partials

Verified: a report with an R code block renders with working syntax
highlighting and full branding.

R/quarto.R

@@ -135,12 +135,12 @@ use_civilytics_theme <- function(path = ".", force = FALSE) {
     .copy_pkg_file(file.path("quarto/latex", f), file.path("latex", f), path, force)
   }
 
-  # Typst
-  .copy_pkg_file(
-    "quarto/typst/civilytics-typst.typ",
-    "typst/civilytics-typst.typ",
-    path, force
-  )
+  # Typst — shipped as template-partials so Quarto keeps its Skylighting
+  # definitions and syntax-highlighted code blocks render (see issue #12)
+  typst_files <- c("typst-template.typ", "typst-show.typ")
+  for (f in typst_files) {
+    .copy_pkg_file(file.path("quarto/typst", f), file.path("typst", f), path, force)
+  }
 
   # Logos — for _brand.yml (expects assets/logo/)
   .copy_logos("assets/logo", path, force)
@@ -158,7 +158,9 @@ use_civilytics_theme <- function(path = ".", force = FALSE) {
   message("    include-in-header: latex/civilytics.tex")
   message("    include-before-body: latex/civilytics-title.tex")
   message("  typst:")
-  message("    template: typst/civilytics-typst.typ")
+  message("    template-partials:")
+  message("      - typst/typst-template.typ")
+  message("      - typst/typst-show.typ")
   message("---")
   message("\nSee examples/report.qmd for a complete example.")
   invisible(NULL)