fix(telegram): add block streaming coalesce defaults to prevent message splitting

Telegram was the only channel missing blockStreamingCoalesceDefaults
in its plugin config. Every other channel (Slack, Discord, Mattermost,
Google Chat, Signal) sets { minChars: 1500, idleMs: 1000 } so the
coalescer buffers small block-streamed fragments before flushing them
as separate messages. Without these defaults, Telegram fell back to
the global minimum (800 chars / 1s idle), causing short streamed
paragraphs to be sent as individual messages instead of being merged.

Fixes #47454

extensions/telegram/src/shared.ts

@@ -95,6 +95,9 @@ export function createTelegramPluginBase(params: {
       nativeCommands: true,
       blockStreaming: true,
     },
+    streaming: {
+      blockStreamingCoalesceDefaults: { minChars: 1500, idleMs: 1000 },
+    },
     reload: { configPrefixes: ["channels.telegram"] },
     configSchema: buildChannelConfigSchema(TelegramConfigSchema),
     config: {