Build an HTML5 tower defense demo (single file).
Theme: circuit board grid with neon traces.
Map: fixed path with 8-12 nodes; enemies follow the path.
Towers: 3 types (rapid, splash, slow) with upgrades.
Economy: earn credits per kill; upgrade between waves.
UI: wave timer, credits, lives, selected tower info.
Controls: click grid to place towers; 1/2/3 to switch type; R restart.