Add mouse support to the TUI (tmux-style tile resize)

Enable mouse in the Bubble Tea program. In the layout grid editor:
click a cell to assign a camera, or press on a tile and drag to
resize its span (grid-snapped). Click-to-select on the menu/list
screens and the camera picker. Works over SSH; edits the config,
so it never fights the daemon geometry.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/tui/tui.go

@@ -60,6 +60,11 @@ type model struct {
 	editLayout   int // index into cfg.Layouts for edit/picker screens
 	edCol, edRow int // grid-editor cursor position
 
+	// Mouse drag state for tmux-style tile resizing in the grid editor.
+	dragging  bool
+	dragTile  int
+	dragMoved bool
+
 	status  string
 	isError bool
 }
@@ -71,7 +76,7 @@ func Run(cfgPath string) error {
 		return err
 	}
 	m := &model{cfgPath: cfgPath, cfg: cfg, screen: screenMenu}
-	_, err = tea.NewProgram(m, tea.WithAltScreen()).Run()
+	_, err = tea.NewProgram(m, tea.WithAltScreen(), tea.WithMouseCellMotion()).Run()
 	return err
 }
 
@@ -141,6 +146,8 @@ func (m *model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			m.setStatus("saved to "+m.cfgPath, false)
 		}
 		return m, nil
+	case tea.MouseMsg:
+		return m.handleMouse(msg)
 	case tea.KeyMsg:
 		return m.handleKey(msg)
 	}