Define Module Structure

## Background
For Version 0.1.0 InDev of Tessitura, we need to establish a professional, scalable code architecture with clear separation of concerns. A well-designed module structure is critical for maintainability, testability, and future extension of the application.

## Description
Design and implement the overall code architecture for Tessitura, establishing separate modules with distinct responsibilities and clean interfaces between them. This architecture should follow Rust best practices and create a foundation that will scale as the project grows.

## Requirements
- Create a module structure that separates the following concerns:
- File system operations (directory traversal, metadata collection)
- Data structures (representation of directory hierarchies)
- Display formatting (terminal output, visual rendering)
- Error handling (custom error types, error propagation)
- CLI interface (argument parsing, command execution)
- Configuration management
- Define clean interfaces between modules with minimal coupling
- Document the purpose and responsibility of each module
- Establish patterns for cross-module communication
- Create a consistent error handling strategy across modules

## Technical Notes
- Follow Rust's module system conventions using `mod` declarations
- Consider using the facade pattern for public interfaces
- Use Rust's visibility rules (`pub`, `pub(crate)`, etc.) to control access
- Establish clear dependency directions (which modules can depend on others)
- Consider creating a core library crate separate from the binary
- Define trait interfaces for components that might have multiple implementations
- Use dependency injection patterns where appropriate to improve testability

## Acceptance Criteria
- Codebase is organized into distinct modules with single responsibilities
- Public interfaces between modules are clearly defined and documented
- Module dependencies form a directed acyclic graph (no circular dependencies)
- New functionality can be added without significant architectural changes
- Unit tests can be written for modules in isolation
- Documentation explains the purpose and responsibility of each module
- Code compiles and passes basic functionality tests

## Estimated Effort
High (3-4 days)