feat: Add edit/add functionality in the TUI

[unfunco]

This adds the functionality to add and edit todos from within the TUI, where previously it was only possible to add todos via the CLI. The add/edit form is not perfect, visually it still needs some work and the list selector feels clumsy.

[Copilot]

Pull Request Overview

This PR adds comprehensive edit and add functionality to the TUI, allowing users to create and modify todos directly within the interactive interface. Previously, todos could only be added via the CLI.

Key changes include:

• Addition of form-based UI for adding and editing todos with title, description, and list selection
• Refactoring of storage layer into an interface with improved file handling (atomic writes, proper permissions)
• Introduction of a list definitions package for better abstraction
• Enhanced test coverage for the new functionality

Reviewed Changes

Copilot reviewed 14 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
internal/version/version.go	Updated semantic version to development marker
internal/tui/tui_test.go	Added test helper, fixed spelling, and added comprehensive tests for form functionality
internal/tui/tui.go	Implemented form mode, field navigation, and rendering for add/edit functionality
internal/storage/storage.go	Refactored into interface definition for storage abstraction
internal/storage/file.go	New file-backed storage implementation with atomic writes and secure permissions
internal/storage/file_test.go	Tests for file storage atomicity and permissions
internal/model/todo.go	Added JSON tags and renamed Toggle method to ToggleCompleted
internal/list/list.go	New package defining list metadata and identifiers
internal/cmd/t.go	Updated command to use new storage interface and added title validation
internal/cmd/t_test.go	Tests for title validation logic
go.mod, go.sum	Updated dependencies and moved bubbles/bubbletea to direct dependencies
README.md	Enhanced documentation with installation instructions and clearer examples
.gitignore	Added Claude settings to ignore list
.github/workflows/*.yaml	Restructured CI/PR workflows

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