feat(discord): make gateway optional with REST send path and send logs

Gateway is now an opt-in feature (DISCORD_GATEWAY_ENABLED); when disabled,
messages are delivered via the Discord REST API (discord-rest.ts) instead of
the Durable Object. Record per-route delivery results (send-log.ts) for the
WebUI. Configure assets binding, DO sqlite migration and cron trigger.

src/discord-rest.ts

@@ -0,0 +1,49 @@
+import { log } from "./log";
+
+const DISCORD_API = "https://discord.com/api/v10";
+
+export async function sendMessage(
+  token: string,
+  channelId: string,
+  message: unknown,
+  threadId?: string,
+): Promise<{ ok: boolean; error?: string }> {
+  const url = threadId
+    ? `${DISCORD_API}/channels/${threadId}/messages`
+    : `${DISCORD_API}/channels/${channelId}/messages`;
+
+  for (let attempt = 0; attempt < 3; attempt++) {
+    try {
+      const res = await fetch(url, {
+        method: "POST",
+        headers: {
+          Authorization: `Bot ${token}`,
+          "Content-Type": "application/json",
+        },
+        body: JSON.stringify(message),
+      });
+
+      if (res.status === 429) {
+        const rateLimit = (await res.json()) as { retry_after?: number };
+        const retryAfter = (rateLimit.retry_after ?? 1) * 1000;
+        log.warn({ retryAfter, attempt }, "Rate limited");
+        await new Promise((r) => setTimeout(r, retryAfter));
+        continue;
+      }
+
+      if (!res.ok) {
+        const err = await res.text();
+        log.error({ status: res.status, err, channelId }, "Discord API error");
+        return { ok: false, error: err };
+      }
+
+      return { ok: true };
+    } catch (err) {
+      log.error({ err, attempt, channelId }, "Failed to send message");
+      if (attempt === 2) return { ok: false, error: String(err) };
+      await new Promise((r) => setTimeout(r, 1000 * (attempt + 1)));
+    }
+  }
+
+  return { ok: false, error: "Max retries exceeded" };
+}