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.
Replaced the monolithic pipeline with three dedicated workflows: ci.yml
(build on every push), cd.yml (manual deploy to staging or prod), and
nightly.yml (scheduled build and deploy). This makes it easier to trigger
deploys independently of builds and to diagnose failures.
