Add Bot API 10.2 Communities support example

New CommunitiesBot demonstrating the 36.0.0 communities API:
- onCommunityChatAdded / onCommunityChatRemoved triggers for the
  community_chat_added / community_chat_removed service events
- reading the Community (id/name) from CommunityChatAdded
- ExtendedChat.community (ChatFullInfo.community) via getChat
- waitCommunityChatAdded expectation

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CommunitiesBot/README.md

@@ -0,0 +1,12 @@
+# CommunitiesBot
+
+Demonstrates Communities support introduced in Telegram Bot API 10.2.
+
+Add the bot to a chat that belongs to a community. It reports when the chat is added to or removed from a
+community, and `/community` prints the chat's current community (read from `getChat().community`).
+
+## Launch
+
+```bash
+../gradlew :CommunitiesBot:run --args="BOT_TOKEN"
+```