LPM-138 Refactor Tui with composable modals and use canvas
Refactors the TUI (dashboard + kanban) to use a shared, composable modal system with canvas-based overlay rendering, while consolidating styling into internal/style and expanding issue interactions (e.g., comments).
Changes:
Introduces a new pkg/tui/modal system (manager/stack + multiple modal types) and overlays modals using Lipgloss compositor layers.
Refactors dashboard/kanban views and input handling to use the modal manager + focus manager instead of per-modal boolean state.
Consolidates TUI styling by moving from pkg/tui/styles to internal/style and updates components to use the new style package; adds a shared footer renderer.
copilot suggestion to have consistent checks for all key handlers, to prevent opening for example the edit window and delete window at the same time.. somehow
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
