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/fall/miso-maple-acorn-squash.md

@@ -0,0 +1,14 @@
+*Source: Abby*
+
+## Ingredients
+- Acorn squash, halved
+- Miso paste
+- Maple syrup
+- Butter
+- Sesame seeds
+
+## Instructions
+1. Roast squash halves at 400°F for 30 minutes.
+2. Mix miso, maple syrup, and melted butter.
+3. Brush mixture on squash, roast 10 more minutes.
+4. Garnish with sesame seeds.