refactor: Consolidate external tools and personal configurations under libs/external, clean up libs/common/utils, and update gitignore and AGENTS.md

.gitignore

@@ -100,3 +100,4 @@ logs/
 *.bak
 *.tmp
 backups/gz/
+*.pdf

libs/common/utils/AGENTS.md

@@ -1 +0,0 @@
-我的nvim配置（来自https://github.com/LazyVim/LazyVim），./libs/common/utils/my-nvim

libs/external/AGENTS.md

@@ -4,3 +4,5 @@
 https://github.com/yusufkaraaslan/Skill_Seekers
 
 https://github.com/x1xhlol/system-prompts-and-models-of-ai-tools
+
+我的nvim配置（来自https://github.com/LazyVim/LazyVim），./libs/common/utils/my-nvim