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/sides/cabbage-steaks.md

@@ -0,0 +1,13 @@
+*Source: Matt*
+
+## Ingredients
+- Cabbage, cut into thick slices
+- Olive oil
+- Salt, pepper
+- Garlic powder
+- Optional: balsamic glaze
+
+## Instructions
+1. Brush cabbage steaks with oil, season.
+2. Roast at 400°F for 25-30 minutes, flipping once.
+3. Drizzle with balsamic if desired.