refactor(project): transition to library structure

Move module declarations from src/main.rs to a new src/lib.rs to transition
the project to a library-first structure. This allows other tools and
examples to utilize the core logic.

Co-Authored-By: fiddlerwoaroof/git-smart-commit (gemma-4-31B-it-UD-Q4_K_XL.gguf)

src/lib.rs

@@ -0,0 +1,9 @@
+pub mod command;
+pub mod draw;
+pub mod format;
+pub mod formula;
+pub mod import;
+pub mod model;
+pub mod persistence;
+pub mod ui;
+pub mod view;

src/main.rs

@@ -1,14 +1,12 @@
-mod command;
-mod draw;
-mod format;
-mod formula;
-mod import;
-mod model;
-mod persistence;
-mod ui;
-mod view;
+use improvise::command;
+use improvise::draw;
+use improvise::import;
+use improvise::model;
+use improvise::persistence;
+use improvise::ui;
+use improvise::view;
 
-use crate::import::csv_parser::csv_path_p;
+use improvise::import::csv_parser::csv_path_p;
 
 use std::path::PathBuf;