Add Gitea Actions deploy workflow and server configuration

- Add basePath /admin to Next.js config for path-based routing
- Add .gitea/workflows/deploy.yml for CI/CD via Gitea Actions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

admin-ui/src/lib/api.ts

@@ -6,6 +6,21 @@
 export const getBaseUrl = () =>
   process.env.NEXT_PUBLIC_RUSTYCMS_API_URL || "http://127.0.0.1:3000";
 
+/**
+ * Expand relative /api/assets/ paths in text (e.g. markdown) to full URLs for preview/display.
+ * Idempotent: already-expanded base URL is preserved.
+ */
+export function expandAssetUrlsInText(text: string, baseUrl: string): string {
+  const base = baseUrl.replace(/\/+$/, "");
+  const fullPrefix = `${base}/api/assets/`;
+  if (!text.includes("/api/assets/")) return text;
+  const placeholder = "\x00__ASSET_BASE__\x00";
+  return text
+    .replaceAll(fullPrefix, placeholder)
+    .replaceAll("/api/assets/", fullPrefix)
+    .replaceAll(placeholder, fullPrefix);
+}
+
 /**
  * Recursively collapse absolute asset URLs to relative paths so the admin
  * keeps and displays /api/assets/... and the backend stores relative.
@@ -14,10 +29,11 @@ export function collapseAssetUrlsForAdmin(
   value: unknown,
   baseUrl: string
 ): unknown {
-  const prefix = `${baseUrl.replace(/\/+$/, "")}/api/assets/`;
+  const base = baseUrl.replace(/\/+$/, "");
+  const prefix = `${base}/api/assets/`;
   if (typeof value === "string") {
-    if (value.startsWith(prefix)) return `/api/assets/${value.slice(prefix.length)}`;
-    return value;
+    if (!value.includes(prefix)) return value;
+    return value.replaceAll(prefix, "/api/assets/");
   }
   if (Array.isArray(value)) return value.map((v) => collapseAssetUrlsForAdmin(v, baseUrl));
   if (value != null && typeof value === "object") {