Standardize code formatting across all 173 Rust source files
using rustfmt. No functional changes - purely cosmetic.
This establishes a consistent code style baseline for the
project going forward.
Add server-side routes for /profile, /admin, and /shared that
serve their respective HTML pages directly (same pattern already
used for /login). Updated all frontend references to use clean
URLs instead of .html extensions.
Fixes#99
Dionisio