feat: add Telegram push support with multi-target routes

Add a platform-aware route target system so a single route can forward
to several destinations at once (e.g. a Discord channel and a Telegram
group). Route.target becomes Route.targets[] with per-entry platform,
channelId/threadId for Discord and chatId/topicId for Telegram; the
legacy single-target format is normalized on load and accepted by the
admin API.

Implement the Telegram driver with HTML rendering and Bot API
sendMessage (chat_id + message_thread_id for topics, retry on 429/5xx),
plus /gh commands served over POST /telegram/webhook: login, logout,
comment, merge and close. The comment/merge/close commands resolve the
issue or PR from the replied-to notification message. OAuth binding now
stores a D1 telegram_links mapping and replies with a confirmation.

Sync the Telegram webhook from the scheduled trigger via setWebhook.

src/drivers/telegram/render.ts

@@ -0,0 +1,45 @@
+import type { NeutralMessage } from "../../types";
+
+function esc(s: string): string {
+  return s
+    .replace(/&/g, "&")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;");
+}
+
+function inlineUrl(url?: string, text?: string): string {
+  const label = esc(text ?? url ?? "");
+  if (!url) return label;
+  return `<a href="${esc(url)}">${label}</a>`;
+}
+
+export function renderNeutralMessage(message: NeutralMessage): string {
+  const parts: string[] = [];
+  const title = inlineUrl(message.url, message.title);
+  parts.push(`<b>${title}</b>`);
+
+  if (message.author) {
+    const author = message.author.url
+      ? `<a href="${esc(message.author.url)}">${esc(message.author.name)}</a>`
+      : esc(message.author.name);
+    parts.push(`👤 ${author}`);
+  }
+
+  if (message.description) {
+    parts.push(esc(message.description));
+  }
+
+  for (const field of message.fields ?? []) {
+    parts.push(`<b>${esc(field.name)}</b>: ${esc(field.value)}`);
+  }
+
+  const meta: string[] = [];
+  if (message.footer) meta.push(esc(message.footer));
+  if (message.timestamp) meta.push(esc(message.timestamp));
+  if (meta.length > 0) {
+    parts.push(`<i>${meta.join(" · ")}</i>`);
+  }
+
+  return parts.join("\n");
+}