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/view.go

@@ -106,6 +106,7 @@ func (m *model) viewLayoutEdit() string {
 	b.WriteString(m.renderGrid(cols, rows))
 	b.WriteString("\n\n")
 	b.WriteString(strings.Join([]string{
+		hkey("click", "assign cell") + "    " + hkey("drag a tile", "resize") + "  (mouse)",
 		hkey("←↑↓→/hjkl", "move") + "    " + hkey("enter", "assign") + "    " + hkey("c", "clear"),
 		"resize tile  " + hkey("L/H", "wider/narrower") + "    " + hkey("J/K", "taller/shorter"),
 		"base grid  " + hkey("] [", "cols") + "    " + hkey("} {", "rows") + "    " + hkey("esc", "back"),