Split the app into subapps, adding categories to it

[fillipe-gsm]

Handles #10

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This pull request does two things:

• It creates a new categories sub-app to the main app;
• It splits the original tasks into its own sub-app tasks as well.

This adds a breaking change to everything, so now the previous kanban-cli add should become kanban-cli tasks add and so on.

[Copilot]

Pull Request Overview

This PR restructures the application by splitting functionality into separate sub-apps for tasks and categories, introducing a breaking CLI change where commands now require a subcommand prefix (e.g., kanban-cli tasks add instead of kanban-cli add).

Key Changes:

• Moved the Category model from src/tasks/models/ to a new src/categories/models/ module
• Created a new categories sub-app with CRUD operations for category management
• Refactored the main app to register both tasks and categories as separate Typer sub-applications

Reviewed Changes

Copilot reviewed 34 out of 42 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/app/app.py	Refactored to register tasks and categories as sub-apps instead of direct commands
src/tasks/tasks_app.py	New file extracting task-related commands into a separate Typer app
src/categories/categories_app.py	New file implementing category management commands
src/categories/models/category.py	Moved from tasks module and added new methods for listing and editing
src/categories/controllers/*.py	New controllers for category CRUD operations
src/categories/presenters/*.py	New presenters for category-related UI output
src/tasks/models/task.py	Updated import path for Category model
tests/**/*.py	Updated import paths and test invocations to match new app structure

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