chore: replace skills/ with notte-skills submodule (#37)

Author: andreakiro

.github/workflows/test-skills.yml

@@ -0,0 +1,4 @@
+[submodule "notte-skills"]
+	path = notte-skills
+	url = https://github.com/nottelabs/notte-skills.git
+	branch = main

.gitmodules

@@ -393,7 +393,7 @@ Core workflow:
 
 ### Skills Documentation
 
-For comprehensive documentation including templates and reference guides, see the [skills/notte-browser](skills/notte-browser/SKILL.md) folder.
+For comprehensive documentation including templates and reference guides, see the [notte-skills/plugins/notte-cli/skills/notte-browser](notte-skills/plugins/notte-cli/skills/notte-browser/SKILL.md) folder (vendored as a submodule from [nottelabs/notte-skills](https://github.com/nottelabs/notte-skills)).
 
 ## Security