feat: sync Bot API gateway support

cmd/bots/ptbecho/README.md

@@ -0,0 +1,49 @@
+# python-telegram-bot echo demo
+
+This demo uses the normal `python-telegram-bot` API and only swaps the Bot API
+base URLs to telesrv.
+
+```powershell
+python -m pip install python-telegram-bot
+$env:TELESRV_BOT_TOKEN = "<bot_id>:<secret>"
+python .\cmd\bots\ptbecho\echo.py `
+  --base-url http://127.0.0.1:8081/bot `
+  --base-file-url http://127.0.0.1:8081/file/bot
+```
+
+In a group with BotFather privacy enabled, send a command such as:
+
+```text
+/ping hello from group
+```
+
+主动发送一条消息并退出：
+
+```powershell
+python .\cmd\bots\ptbecho\echo.py `
+  --send-only `
+  --send-chat-id -1000000000002 `
+  --send-text "hello from python-telegram-bot"
+```
+
+长轮询 echo 启动后立即主动发送一条消息：
+
+```powershell
+python .\cmd\bots\ptbecho\echo.py `
+  --send-chat-id -1000000000002 `
+  --send-text "ptbecho is online"
+```
+
+可选参数：
+
+- `--send-count N`：连续主动发送 N 条。
+- `--send-interval SEC`：连续发送之间的间隔。
+- `TELESRV_BOT_DEMO_CHAT_ID` / `TELESRV_BOT_DEMO_SEND_TEXT`：主动发送参数的环境变量形式。
+
+本地超级群 chat id 使用 Bot API 形式 `-100<channel_id>`；例如 channel id 为
+`2` 时是 `-1000000000002`。
+
+Implemented telesrv Bot API surface for this demo: `getMe`, `getUpdates`,
+`deleteWebhook`, `sendMessage`, and file URL configuration. The wider gateway
+also has basic `sendPhoto`, `sendDocument`, `editMessageText`, `deleteMessage`,
+`answerCallbackQuery`, `getFile`, and `/file/bot...` support.