docs(platforms): HTTP Bot adapter tutorial (zh/en/ja) (#98)

* docs(platforms): add HTTP Bot adapter tutorial (zh/en/ja)

Server-to-server HTTP integration guide for the new http_bot platform
adapter: signed inbound webhook, signed outbound callbacks, N->1 aggregation,
1->M multi-reply, session reset, sync convenience mode, error codes, and a
5-minute reference-client demo. Registered in docs.json nav for all three
locales; adds the platform icon.

* docs(http-bot): link the interactive playground in all locales

Add a section pointing at examples/http-bot/playground.py (browser debug
console: sign -> POST -> 202 -> live callbacks) ahead of the CLI reference
clients, in zh/en/ja.

* style(platforms): use </> code icon for http-bot logo

docs.json

@@ -270,6 +270,7 @@
                   "en/usage/platforms/slack",
                   "en/usage/platforms/line",
                   "en/usage/platforms/webpage",
+                  "en/usage/platforms/http-bot",
                   "en/usage/platforms/kook",
                   "en/usage/platforms/lark",
                   "en/usage/platforms/dingtalk",
@@ -526,7 +527,8 @@
                   "zh/usage/platforms/telegram",
                   "zh/usage/platforms/slack",
                   "zh/usage/platforms/line",
-                  "zh/usage/platforms/webpage"
+                  "zh/usage/platforms/webpage",
+                  "zh/usage/platforms/http-bot"
                 ]
               },
               {
@@ -719,6 +721,7 @@
                   "ja/usage/platforms/slack",
                   "ja/usage/platforms/line",
                   "ja/usage/platforms/webpage",
+                  "ja/usage/platforms/http-bot",
                   "ja/usage/platforms/kook",
                   "ja/usage/platforms/lark",
                   "ja/usage/platforms/dingtalk",