feat(docs): add documentation site and demo features

- Introduced a new documentation site for Cursor BYOK using Next.js and Fumadocs.
- Added a product demo page with a corresponding Vite configuration.
- Implemented a demo API to simulate LLM calls and responses.
- Enhanced the Makefile to include new build and development commands for the documentation.
- Updated package.json scripts for building and running the documentation site.
- Created various components and layouts for the documentation structure, including blog and user documentation sections.
- Added styling for the new components and layouts to ensure a cohesive design.
- Included a README and other necessary files for local development and deployment.

apps/docs/scripts/build-product-demo.mjs

@@ -0,0 +1,18 @@
+import { existsSync } from 'node:fs';
+import { spawnSync } from 'node:child_process';
+import { fileURLToPath } from 'node:url';
+import path from 'node:path';
+
+const docsRoot = path.dirname(fileURLToPath(new URL('../package.json', import.meta.url)));
+const desktopRoot = path.resolve(docsRoot, '../desktop');
+const npm = process.platform === 'win32' ? 'npm.cmd' : 'npm';
+const vite = path.join(desktopRoot, 'node_modules', '.bin', process.platform === 'win32' ? 'vite.cmd' : 'vite');
+
+if (!existsSync(vite)) run(['ci'], desktopRoot);
+run(['run', 'build:demo'], desktopRoot);
+
+function run(args, cwd) {
+  const result = spawnSync(npm, args, { cwd, stdio: 'inherit' });
+  if (result.error) throw result.error;
+  if (result.status !== 0) process.exit(result.status ?? 1);
+}