Merge pull request #73 from LazyBachelor/LPM-138

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.

internal/utils/user/user.go

@@ -0,0 +1,19 @@
+package user
+
+import (
+	"os"
+	"os/user"
+)
+
+func GetOsUsername() string {
+	if u, err := user.Current(); err == nil && u.Username != "" {
+		return u.Username
+	}
+	if s := os.Getenv("USER"); s != "" {
+		return s
+	}
+	if s := os.Getenv("USERNAME"); s != "" {
+		return s
+	}
+	return "user"
+}