feat(docs-site): syntax-highlight examples and restyle the site

The manual is authored man-page style: every synopsis, example, option
table, and description sits in one 4-space-indented block. On the site
that renders as a single unhighlighted grey slab, because an indented
block declares no language.

Split each block into its paragraphs at site-build time and classify
them: synopsis and shell examples become ```fish fences, descriptions
become real prose, and column-aligned reference tables keep their
indentation. 175 blocks now highlight; the 412 lines of genuine tables
are left alone.

The transform is site-only. docs/manual/** keeps the indented form the
pandoc man-page pipeline and config-help depend on, and a test enforces
that no fence is ever written back to the SSOT.

Also:
- Point Expressive Code at the bundled Catppuccin Mocha/Latte themes so
  code blocks match the palette in catppuccin.css.
- Build the functions sidebar group explicitly. `autogenerate` labelled
  it with the raw directory slug and republished the directory index as
  a child of the group it already titled, producing the duplicate
  "Functions Reference" row.
- Skip `Synopsis:` lines when deriving card descriptions; they restated
  the calling convention the card already shows as its title.
- Widen the palette: tinted heading levels, inline code, links, card
  hover accents, aside accents, and table headers.

Fixes a bug where _split_entries stripped the leading indentation of an
entry's first line, detaching `Synopsis:` from the block it opens.

docs/site/astro.config.mjs

@@ -16,6 +16,16 @@ export default defineConfig({
         },
       ],
       customCss: ['./src/styles/catppuccin.css'],
+      expressiveCode: {
+        // Shiki ships both Catppuccin flavours; Starlight picks by the
+        // reader's colour scheme, matching the palette in catppuccin.css.
+        themes: ['catppuccin-mocha', 'catppuccin-latte'],
+        styleOverrides: {
+          borderRadius: '0.4rem',
+          borderColor: 'var(--sl-color-gray-5)',
+          codeFontSize: '0.875rem',
+        },
+      },
       sidebar,
     }),
   ],