♻️ Restructure: Move Astro to repository root

BREAKING CHANGE: Astro project is now at repository root
- Removed dealplustech-astro subdirectory
- Moved all Astro files to root
- Updated PostCSS config to .cjs
- Removed old Next.js files

✅ 11 pages built successfully
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✅ Ready for Easypanel deployment (no root dir needed)

Migration path:
- Old structure: /dealplustech-astro/
- New structure: / (root)

dealplustech-astro/node_modules/retext-stringify/lib/index.d.ts

@@ -1,8 +0,0 @@
-/**
- * Add support for serializing natural language.
- *
- * @returns {undefined}
- *   Nothing.
- */
-export default function retextStringify(): undefined;
-export type Root = import('nlcst').Root;

dealplustech-astro/node_modules/retext-stringify/lib/index.js

@@ -1,27 +0,0 @@
-/**
- * @typedef {import('nlcst').Root} Root
- */
-
-import {toString} from 'nlcst-to-string'
-
-/**
- * Add support for serializing natural language.
- *
- * @returns {undefined}
- *   Nothing.
- */
-export default function retextStringify() {
-  // eslint-disable-next-line unicorn/no-this-assignment
-  const self =
-    /** @type {import('unified').Processor<undefined, undefined, undefined, Root, string>} */ (
-      // @ts-expect-error -- TS in JSDoc doesn’t understand `this`.
-      this
-    )
-
-  self.compiler = compiler
-}
-
-/** @type {import('unified').Compiler<Root, string>} */
-function compiler(tree) {
-  return toString(tree)
-}