feat(proxy): add environment config and request handling

- Introduce environment-based configuration for proxy settings
- Add middleware for API key authentication
- Implement request forwarding to LanguageTool backend
- Set up server startup and routing logic

src/ltProxyHandler.ts

@@ -0,0 +1,28 @@
+import { Handler } from 'http-kernel/Types/mod.ts';
+import { Env } from './env.ts';
+
+/**
+ * Forwards the incoming request to the actual LanguageTool server.
+ * Dynamically passes through path and query string.
+ */
+export const handler: Handler = async (ctx) => {
+    const originalUrl = new URL(ctx.req.url);
+    const proxyUrl = new URL(
+        `${originalUrl.pathname}${originalUrl.search}`,
+        `http://${Env.ltServerHost}:${Env.ltServerPort}`,
+    );
+
+    const forwarded = await fetch(proxyUrl.toString(), {
+        method: ctx.req.method,
+        headers: ctx.req.headers,
+        body: ctx.req.body,
+    });
+
+    const headers = new Headers(forwarded.headers);
+    return new Response(forwarded.body, {
+        status: forwarded.status,
+        headers,
+    });
+};
+
+export { handler as ltProxyHandler };