refactor(wechat_kf): rename channel from wechatcom_kf and split corp_id

Rename the WeCom customer-service channel and give it its own corp_id
field so users no longer have to share `wechatcom_corp_id` with the
self-built WeCom app channel.

Renames (channel-side):
- channel type / const: wechatcom_kf -> wechat_kf
- package dir: channel/wechatcom_kf/ -> channel/wechat_kf/
- python files / classes: WechatComKf* -> WechatKf*
- config keys: wechatcom_kf_{secret,token,aes_key,port} ->
  wechat_kf_{secret,token,aes_key,port}; new wechat_kf_corp_id
- env vars: WECHATCOM_KF_* -> WECHAT_KF_*; new WECHAT_KF_CORP_ID
- log prefix / cursor file: [wechatcom_kf] -> [wechat_kf]
- web console CHANNEL_DEFS key + startup log line

Renames (docs):
- docs/channels/wecom-kf.mdx -> docs/channels/wechat-kf.mdx (zh/en/ja)
- update docs.json sidebar entries and all field names inside the docs

In addition, the Web Console "微信客服" entry now exposes its own
Corp ID field instead of reusing the wechatcom_app one, and includes
the screenshot of the visual config in the channel guide.

Web Console onboarding section is added (Tabs: Web Console / config
file) and the local URL `http://127.0.0.1:9899/` parenthetical is
dropped for consistency with other channel docs.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/docs.json

@@ -188,7 +188,7 @@
                   "channels/wecom-bot",
                   "channels/qq",
                   "channels/wecom",
-                  "channels/wecom-kf",
+                  "channels/wechat-kf",
                   "channels/wechatmp"
                 ]
               }
@@ -381,7 +381,7 @@
                   "en/channels/wecom-bot",
                   "en/channels/qq",
                   "en/channels/wecom",
-                  "en/channels/wecom-kf",
+                  "en/channels/wechat-kf",
                   "en/channels/wechatmp"
                 ]
               }
@@ -576,7 +576,7 @@
                   "ja/channels/wecom-bot",
                   "ja/channels/qq",
                   "ja/channels/wecom",
-                  "ja/channels/wecom-kf",
+                  "ja/channels/wechat-kf",
                   "ja/channels/wechatmp"
                 ]
               }