refactor: move config dir to ~/.config/hy3d, replace skill with run-hy3d

- config dir renamed hunyuan3dweb -> hy3d (cookies/profile moved intact,
  auth re-verified: quota 20/20)
- cli.py/login.py/READMEs/doc paths updated to ~/.config/hy3d
- skill: delete run-hunyuan3dweb, add run-hy3d pointing at bin/hy3d
- zero stale old-name references remain (one historical note in skill)

doc/api.md

@@ -8,7 +8,7 @@
 
 Cookie 会话认证。登录后由浏览器自动携带 `sessionid` 等 Cookie。
 
-持久化数据保存在 `~/.config/hunyuan3dweb/profile`，CloakBrowser 复用该目录即可保持登录态。
+持久化数据保存在 `~/.config/hy3d/profile`，CloakBrowser 复用该目录即可保持登录态。
 
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