Initial Mebbling hub implementation

app/dashboard/publish-form.tsx

@@ -0,0 +1,34 @@
+"use client";
+
+import { FormEvent, useState } from "react";
+
+type Source = { id: number; name: string };
+
+export function PublishForm({ sources }: { sources: Source[] }) {
+  const [error, setError] = useState("");
+  const [submitting, setSubmitting] = useState(false);
+
+  async function submit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitting(true); setError("");
+    try {
+      const response = await fetch("/api/posts", { method: "POST", body: new FormData(event.currentTarget), headers: { Accept: "application/json" } });
+      const result = await response.json();
+      if (!response.ok) throw new Error(result.error || "發佈失敗");
+      window.location.assign(`/posts/${result.id}`);
+    } catch (reason) {
+      setError(reason instanceof Error ? reason.message : "發佈失敗");
+      setSubmitting(false);
+    }
+  }
+
+  return <form onSubmit={submit} encType="multipart/form-data">
+    <label>內容（Markdown）<textarea name="content" required /></label>
+    <label>標籤（逗號分隔）<input name="tags" placeholder="旅行, 想法" /></label>
+    <label>可見性<select name="visibility" defaultValue="PUBLIC"><option value="PUBLIC">公開</option><option value="PROTECTED">受保護</option><option value="PRIVATE">私人</option></select></label>
+    <label>發佈來源<select name="sourceId" required>{sources.map((source) => <option key={source.id} value={source.id}>{source.name}</option>)}</select></label>
+    <label>圖片或附件（每檔最多 10 MB）<input name="attachments" type="file" multiple /></label>
+    {error && <p className="error">{error}</p>}
+    <button disabled={submitting}>{submitting ? "發佈中…" : "發佈並同步"}</button>
+  </form>;
+}