Upgrade to Astro 7 and fix breaking changes

Bumps astro to ^7.0.9 and @astrojs/mdx to ^7.0.3, and resolves the
breaking changes surfaced by the upgrade:

- Header.astro: mark the theme-switcher <script> as `is:inline`. Astro 7
  hands non-inline scripts to Vite for bundling, which cannot resolve the
  `/docs/js/modules/theme-switcher.js` public asset and failed the build.
  Inlining emits it verbatim so the browser resolves it at runtime.

- astro.config.mjs: move remark plugins from the deprecated
  `markdown.remarkPlugins` into `markdown.processor: unified({ ... })`
  from @astrojs/markdown-remark (added as a direct dependency since it is
  now imported by the config). `trailingSlash` was not honored in its location, so it was removed, and drop the dead `extendDefaultPlugins`.

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

Author: borland

astro.config.mjs

@@ -1,6 +1,7 @@
 import remarkDirective from 'remark-directive';
 import remarkHeading from 'remark-heading-id';
 import { defineConfig } from 'astro/config';
+import { unified } from '@astrojs/markdown-remark';
 import mdx from '@astrojs/mdx';
 import { attributeMarkdown, wrapTables } from '/src/themes/octopus/utilities/custom-markdown.mjs';
 import llmMdEmitter from './src/integrations/llm-md-emitter.ts';
@@ -16,14 +17,14 @@ export default defineConfig({
         shikiConfig: {
             theme: 'light-plus'
         },
-        remarkPlugins: [
-            remarkDirective,
-            remarkHeading,
-            attributeMarkdown,
-            wrapTables
-        ],
-        trailingSlash: 'never',
-        extendDefaultPlugins: true,
+        processor: unified({
+            remarkPlugins: [
+                remarkDirective,
+                remarkHeading,
+                attributeMarkdown,
+                wrapTables
+            ],
+        }),
     },
     server: {
         port: 3000

package.json

@@ -28,8 +28,9 @@
         "watch": "onchange 'src/**/*.{js,mjs,ts,astro,css}' 'public/docs/js/**/*.js' 'public/docs/css/**/*.css' -- prettier --write --plugin=prettier-plugin-astro {{changed}}"
     },
     "dependencies": {
-        "@astrojs/mdx": "^5.0.4",
-        "astro": "^6.3.1",
+        "@astrojs/markdown-remark": "7.2.1",
+        "@astrojs/mdx": "^7.0.3",
+        "astro": "^7.0.9",
         "astro-accelerator-utils": "^0.3.84",
         "glob": "^13.0.6",
         "gray-matter": "^4.0.3",