init(docs): create docs site template with Fumapress and Waku

docs/src/app.css

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+@import "tailwindcss";
+@import "fumadocs-ui/css/neutral.css";
+@import "fumadocs-ui/css/preset.css";
+@import "fumapress/css/preset.css";
+
+/* Fonts — self-hosted via Fontsource, referenced by the typeset presets. */
+@import "@fontsource-variable/dm-sans";
+@import "@fontsource-variable/instrument-sans";
+@import "@fontsource-variable/jetbrains-mono";
+
+/* shadcn/typeset — one CSS file you own.
+   Regenerate it any time at https://ui.shadcn.com/typeset */
+@import "./typeset.css";
+
+:root {
+  --font-dm-sans: "DM Sans Variable", sans-serif;
+  --font-instrument-sans: "Instrument Sans Variable", sans-serif;
+  --font-jetbrains-mono: "JetBrains Mono Variable", monospace;
+}
+
+@theme inline {
+  --default-font-family: var(--font-instrument-sans);
+  --font-heading: var(--font-dm-sans);
+  --font-mono: var(--font-jetbrains-mono);
+}
+
+/* ---------------------------------------------------------
+   Typeset presets — tune rhythm per context.
+   Three controls: size, leading, flow.
+   Built with https://ui.shadcn.com/typeset
+   --------------------------------------------------------- */
+
+.typeset-docs {
+  --typeset-font-body: var(--font-instrument-sans);
+  --typeset-font-heading: var(--font-dm-sans);
+  --typeset-font-mono: var(--font-jetbrains-mono);
+  --typeset-size: 16px;
+  --typeset-leading: 1.9;
+  --typeset-flow: 1em;
+}
+
+/* Tighter rhythm, e.g. for changelog callouts or chat-like UI */
+.typeset-compact {
+  --typeset-leading: 1.6;
+  --typeset-flow: 1em;
+}
+
+/* Measure (80ch) — the builder puts max-width on the wrapper,
+   not in typeset.css. Add this class next to `typeset` when your
+   layout doesn't already constrain line length. */
+.typeset-measure {
+  max-width: 37em;
+}
+
+/* ---------------------------------------------------------
+   Fumadocs interop:
+   Fumadocs UI ships its own `prose` styling for page bodies.
+   When a container is both, let Typeset own the rhythm by
+   disabling the prose margins that would double up.
+   Keep interactive Fumadocs components (tabs, callouts,
+   accordions) out of Typeset with `not-typeset`.
+   --------------------------------------------------------- */
+.typeset.prose :where(*) {
+  margin-block-end: 0;
+}