fix(telegram): sanitize outbound markdown for legacy parse mode

The @chat-adapter/telegram adapter hardcodes parse_mode=Markdown (legacy)
but its converter emits CommonMark. Messages containing **bold** or list
bullets that round-trip to `*` produce "can't parse entities" errors and
get dropped after retries.

Add an opt-in transformOutboundText hook on the chat-sdk bridge and wire
a Telegram-specific sanitizer that downgrades **bold** to *bold*, rewrites
dash/plus list bullets to a Unicode bullet so the adapter's re-stringify
doesn't inject stray `*`, and strips unbalanced delimiters or brackets.
Only Telegram opts in; other channels are unaffected.

Workaround until upstream (vercel/chat) ships mode-aware conversion —
PR #367 adds a parseMode knob but not the converter fix.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/channels/telegram.ts

@@ -9,6 +9,7 @@ import { readEnvFile } from '../env.js';
 import { log } from '../log.js';
 import { createMessagingGroup, getMessagingGroupByPlatform, updateMessagingGroup } from '../db/messaging-groups.js';
 import { createChatSdkBridge, type ReplyContext } from './chat-sdk-bridge.js';
+import { sanitizeTelegramLegacyMarkdown } from './telegram-markdown-sanitize.js';
 import { registerChannelAdapter } from './channel-registry.js';
 import type { ChannelAdapter, ChannelSetup, InboundMessage } from './adapter.js';
 import { tryConsume } from './telegram-pairing.js';
@@ -155,6 +156,7 @@ registerChannelAdapter('telegram', {
       concurrency: 'concurrent',
       extractReplyContext,
       supportsThreads: false,
+      transformOutboundText: sanitizeTelegramLegacyMarkdown,
     });
 
     const botUsernamePromise = fetchBotUsername(token);