feat: implement icon directive with relative path fallback

Refactor icon rendering to use a custom `marked-directive` instead of
a global icon prefix. This allows icons to use a CSS-based fallback
chain (searching up to 10 directory levels for an `assets/` folder),
making icon paths more robust and removing the need to pass path
prefixes through the component tree.

src/components/md-embed.tsx

@@ -1,5 +1,5 @@
 import { customElement, noShadowDOM } from "solid-element";
-import { createResource, Show, createMemo, createEffect } from "solid-js";
+import { createResource, Show, createEffect } from "solid-js";
 import { getIndexedData } from "../data-loader/file-index";
 import { extractSection } from "../data-loader";
 import { parseMarkdown } from "../markdown";
@@ -27,9 +27,6 @@ customElement("md-embed", { headingBase: 0 }, (props, { element }) => {
   const articlePath = articleEl?.getAttribute("data-src") || "";
   const resolvedPath = resolvePath(articlePath, filePath);
 
-  // 计算嵌入文件的 iconPrefix，用 createMemo 包装避免每个 embed 都重新计算
-  const iconPrefix = createMemo(() => resolvePath(resolvedPath, "./assets"));
-
   const [content] = createResource(
     () => ({ path: resolvedPath, section }),
     async ({ path, section }) => {
@@ -56,10 +53,7 @@ customElement("md-embed", { headingBase: 0 }, (props, { element }) => {
       </Show>
       <Show when={!content.loading && !content.error && content()}>
         {/* biome-ignore lint/security/noDangerouslySetInnerHtml: markdown render */}
-        <div
-          class="prose"
-          innerHTML={parseMarkdown(content()!, iconPrefix())}
-        />
+        <div class="prose" innerHTML={parseMarkdown(content()!)} />
       </Show>
     </div>
   );