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/__tests__/telegram.test.ts

@@ -0,0 +1,92 @@
+import { describe, it, expect, afterEach } from "bun:test";
+import { sendMessage } from "../drivers/telegram/rest";
+import { renderNeutralMessage } from "../drivers/telegram/render";
+import type { NeutralMessage } from "../types";
+
+function mockFetch(handler: (url: string, init?: RequestInit) => Response): void {
+  globalThis.fetch = (input: RequestInfo | URL, init?: RequestInit): Promise<Response> =>
+    Promise.resolve(handler(String(input), init));
+}
+
+const restoredFetch = globalThis.fetch;
+
+afterEach(() => {
+  globalThis.fetch = restoredFetch;
+});
+
+describe("telegram renderNeutralMessage", () => {
+  it("renders title, fields and footer as HTML", () => {
+    const message: NeutralMessage = {
+      title: "acme/widget: Add feature",
+      url: "https://github.com/acme/widget",
+      fields: [{ name: "Status", value: "success" }],
+      footer: "acme/widget",
+    };
+    const out = renderNeutralMessage(message);
+    expect(out).toContain('<b><a href="https://github.com/acme/widget">acme/widget: Add feature</a></b>');
+    expect(out).toContain("<b>Status</b>: success");
+    expect(out).toContain("<i>acme/widget</i>");
+  });
+
+  it("escapes HTML special characters", () => {
+    const out = renderNeutralMessage({
+      title: "a <b> & \"c\"",
+      fields: [{ name: "body", value: "<script>alert(1)</script>" }],
+    });
+    expect(out).not.toContain("<b>acme");
+    expect(out).toContain("&lt;script&gt;alert(1)&lt;/script&gt;");
+  });
+});
+
+describe("telegram-rest sendMessage", () => {
+  it("posts to the bot API with chat_id and parse_mode", async () => {
+    let capturedUrl = "";
+    let capturedInit: RequestInit | undefined;
+    mockFetch((url, init) => {
+      capturedUrl = url;
+      capturedInit = init;
+      return new Response(JSON.stringify({ ok: true, result: { message_id: 42 } }), {
+        status: 200,
+      });
+    });
+
+    const result = await sendMessage("token-abc", "-100123", "hello");
+
+    expect(result.ok).toBe(true);
+    expect(result.messageId).toBe("42");
+    expect(capturedUrl).toBe("https://api.telegram.org/bottoken-abc/sendMessage");
+    const body = JSON.parse(String(capturedInit!.body)) as Record<string, unknown>;
+    expect(body.chat_id).toBe("-100123");
+    expect(body.parse_mode).toBe("HTML");
+    expect(body.message_thread_id).toBeUndefined();
+  });
+
+  it("includes message_thread_id when topicId is given", async () => {
+    let capturedInit: RequestInit | undefined;
+    mockFetch((_url, init) => {
+      capturedInit = init;
+      return new Response(JSON.stringify({ ok: true, result: { message_id: 1 } }), {
+        status: 200,
+      });
+    });
+
+    await sendMessage("t", "-100123", "hello", "999");
+    const body = JSON.parse(String(capturedInit!.body)) as Record<string, unknown>;
+    expect(body.message_thread_id).toBe(999);
+  });
+
+  it("returns error on non-ok response", async () => {
+    mockFetch(() =>
+      new Response(JSON.stringify({ ok: false, description: "chat not found" }), { status: 400 }),
+    );
+    const result = await sendMessage("t", "-100123", "hello");
+    expect(result.ok).toBe(false);
+    expect(result.error).toContain("chat not found");
+  });
+
+  it("returns error when token is missing", async () => {
+    const result = await sendMessage("", "-100123", "hello");
+    expect(result.ok).toBe(false);
+    expect(result.errorCode).toBe("NO_TOKEN");
+  });
+});