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)

README_REVERSE_ENGINEERING.md

@@ -90,8 +90,8 @@ resource_url = upload_image("/path/to/image.png")
 ```bash
 hy3d-login
 # Follow prompts to enter email and verification code
-# Login state is automatically saved to ~/.config/hunyuan3dweb/profile
-# Cookies are also exported to ~/.config/hunyuan3dweb/cookies.txt
+# Login state is automatically saved to ~/.config/hy3d/profile
+# Cookies are also exported to ~/.config/hy3d/cookies.txt
 ```
 
 **Login State Detection Logic** (dual verification):
@@ -104,7 +104,7 @@ hy3d-login
 ```python
 from hy3d import Hunyuan3DAPI
 
-# Automatically load cookie from ~/.config/hunyuan3dweb/cookies.txt
+# Automatically load cookie from ~/.config/hy3d/cookies.txt
 api = Hunyuan3DAPI()
 
 # Check quota