feat: implement donation form with payment processing

Add main donate page with TMN and PromptPay flows, donation schema
with retry system, SSE integration, heartbeat endpoint, and
file-to-data-url utility. Remove unused donate client component.

app/api/donate/hb/route.ts

@@ -1,10 +1,37 @@
+import { db } from "@/lib/db";
+import { donations } from "@/lib/db/schema";
 import { sse } from "@/lib/db/sse-endpoints";
+import { fileToDataUrl } from "@/lib/utils";
+import { and, asc, not, sql } from "drizzle-orm";
 import { NextRequest } from "next/server";
 
 export async function PATCH(req: NextRequest) {
   const tag = Number(req.nextUrl.searchParams.get("tag") ?? "abc");
   if (Number.isNaN(tag))
     return Response.json({ error: "Invalid Tag" }, { status: 400 });
+
+  queueMicrotask(async () => {
+    const [havent] = await db
+      .select()
+      .from(donations)
+      .where(
+        and(
+          not(donations.sent),
+          sql`${donations.lastPing} < NOW() - INTERVAL '2 minutes'`,
+        ),
+      )
+      .limit(1)
+      .orderBy(asc(donations.id));
+    if (!havent) return;
+    sse.donate.pub("ping", {
+      ...havent,
+      message: havent.message ?? "",
+      image: havent.image
+        ? await fileToDataUrl(new File([Buffer.from(havent.image)], "abc.jpeg"))
+        : undefined,
+    });
+  });
+
   sse.donate.pub("heartbeat", tag);
   return Response.json({ success: true });
 }