chore: remove public/posts to replace with submodule

public/posts/index.json

@@ -1,7 +0,0 @@
-[
-  "20251217-test.md",
-  "20251222-feature-showcase-advanced-mark.md",
-  "20251222-lenovo-xiaoxin-pad-pro-gt-revi.md",
-  "20251223-hey-there.md",
-  "20260103-syntax-highlighting-test.md"
-]