LPM-140 The Sprinting Update
Adds sprint support across the web UI (board + issue detail), TUI kanban, CLI/REPL, and the Beads-backed storage layer.
Changes:
Introduces sprint entities in storage and exposes sprint operations via IssueService.
Updates web board to support backlog vs. sprint columns, sprint selection, and sprint creation routes.
Updates TUI kanban to show backlog + sprint columns and adds sprint selection/creation actions.
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.
