feat!: Split site into public and private sections

Moved the Copper Chronicle and resume into a private git submodule
(src/private), visible only to authenticated users. Added a lock symbol
to the mdbook sidebar for restricted sections. Reorganized nginx/nix
configuration files into a dedicated folder. Removed one-line descriptions
from the menu. Reduced custom CSS to better align the main website's theme
with mdbook's native styling. Personalized the index and blog introduction
pages.

src/recipes/breakfast/german-pancakes.md

@@ -0,0 +1,15 @@
+*Source: Abby*
+
+## Ingredients
+- Eggs
+- Milk
+- Flour
+- Butter
+- Salt
+- Vanilla extract (optional)
+
+## Instructions
+1. Blend eggs, milk, flour, and salt until smooth.
+2. Heat butter in a pan, pour thin layer of batter.
+3. Cook until edges lift, flip and cook other side.
+4. Serve with jam, cream, or savory fillings.