docs: deploy stable and beta docs

docs/.vitepress/theme/custom.css

@@ -1,17 +1,42 @@
 html.dark .light-only {
-	display: none !important;
+  display: none !important;
 }
 
 html:not(.dark) .dark-only {
-	display: none !important;
+  display: none !important;
 }
 
 figure {
-	padding: 1em;
+  padding: 1em;
 }
 
 figcaption {
-	text-align: center;
-	font-size: 0.9em;
-	margin-top: 0.5em;
+  text-align: center;
+  font-size: 0.9em;
+  margin-top: 0.5em;
+}
+
+:root {
+  --vp-layout-top-height: 36px;
+}
+
+.beta-banner {
+  background-color: var(--vp-c-bg);
+  background-image: linear-gradient(var(--vp-c-warning-soft), var(--vp-c-warning-soft));
+  color: var(--vp-c-warning-1);
+  text-align: center;
+  padding: 8px 16px;
+  font-size: 14px;
+  font-weight: 500;
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  z-index: 100;
+}
+
+.beta-banner a {
+  color: var(--vp-c-warning-1);
+  text-decoration: underline;
+  margin-left: 8px;
 }

docs/.vitepress/theme/env.d.ts

@@ -0,0 +1,3 @@
+/// <reference types="vitepress/client" />
+
+declare const __HEADPLANE_BETA_DOCS__: boolean;

docs/.vitepress/theme/index.ts

@@ -1,4 +1,36 @@
-import DefaultTheme from 'vitepress/theme';
-import './custom.css';
+import type { Theme } from "vitepress";
+import DefaultTheme from "vitepress/theme";
+import { h } from "vue";
 
-export default DefaultTheme;
+import "./custom.css";
+
+const beta = __HEADPLANE_BETA_DOCS__ ?? false;
+
+export default {
+  extends: DefaultTheme,
+  Layout() {
+    return h(DefaultTheme.Layout, null, {
+      "layout-top": () =>
+        beta
+          ? h(
+              "div",
+              {
+                class: "beta-banner",
+              },
+              [
+                "You are currently viewing the ",
+                h("strong", "beta"),
+                " documentation for Headplane. ",
+                h(
+                  "a",
+                  {
+                    href: "https://headplane.net",
+                  },
+                  "Go to the stable docs →",
+                ),
+              ],
+            )
+          : null,
+    });
+  },
+} satisfies Theme;