Add error handling with NyxError and refactor console output formatting

- Introduced `NyxError` and `NyxResult` for unified error handling across modules.
- Refactored `scan.rs`, `index.rs`, and `walk.rs` with improved error management and consistent formatting.
- Replaced existing error handling in `database.rs` with `NyxResult`.
- Improved database maintenance by integrating `vacuum` and `clear` methods into workflows.
- Added `dashmap` for efficient parallel diagnostics result aggregation in `scan_with_index_parallel`.
- Enhanced readability and formatting of console outputs in multiple modules.

src/commands/index.rs

@@ -24,8 +24,10 @@ pub fn handle(
             if force || !db_path.exists() {
                 build_index(&project_name, &build_path, &db_path, config)?;
                 println!("✔ {} {}", style("Index built:" ).green(), style(db_path.display()).white().bold());
+                exit(0);
             } else {
                 println!("{} {}", style("↩ Index already exists").yellow(), style("(use --force to rebuild)").dim());
+                exit(0);
             }
         }
         IndexAction::Status { path } => {
@@ -48,7 +50,6 @@ pub fn handle(
             exit(0);
         }
     }
-    Ok(())
 }
 
 pub fn build_index(