feat: complete v0.3 reading and discovery experience

app/api/comments/route.ts

@@ -1,2 +1,17 @@
-import { NextResponse } from "next/server"; import { requireUser } from "@/lib/auth"; import { db } from "@/lib/db"; import { externalUrl } from "@/lib/http";
-export async function POST(req:Request){try{const user=await requireUser();const f=await req.formData();const postId=Number(f.get('postId'));const content=String(f.get('content')||'').trim();if(!postId||!content||content.length>5000)throw new Error('Invalid comment');db.prepare('INSERT INTO comments(post_id,author_id,content) VALUES(?,?,?)').run(postId,user.id,content);return NextResponse.redirect(externalUrl(req,`/posts/${postId}`));}catch{return NextResponse.redirect(externalUrl(req,'/'));}}
+import { NextResponse } from "next/server";
+import { requireUser } from "@/lib/auth";
+import { db } from "@/lib/db";
+import { externalUrl } from "@/lib/http";
+import { notify } from "@/lib/notifications";
+
+export async function POST(req: Request) {
+  try {
+    const user = await requireUser(); const form = await req.formData(); const postId = Number(form.get("postId")); const content = String(form.get("content") || "").trim();
+    if (!postId || !content || content.length > 5000) throw new Error("Invalid comment");
+    const post = db.prepare("SELECT author_id FROM posts WHERE id=? AND hidden=0").get(postId) as { author_id: number } | undefined;
+    if (!post) throw new Error("Post not found");
+    db.prepare("INSERT INTO comments(post_id,author_id,content) VALUES(?,?,?)").run(postId, user.id, content);
+    notify(post.author_id, user.id, postId, "comment", `@${user.username} 留言了你的貼文`);
+    return NextResponse.redirect(externalUrl(req, `/posts/${postId}`));
+  } catch { return NextResponse.redirect(externalUrl(req, "/")); }
+}