Theme and HUD styles

Today was all CSS. I replaced the bare‑bones main.css. Custom properties for the colour palette and the monospace font are in, plus resets, so the whole thing starts from a clean base.

The HUD got the bulk of the work: wordmark, status dot, UTC clock, telemetry panels, legend rows, live feed, layer controls, detail card, and the boot screen are all styled. Added responsive breakpoints for narrower viewports so the panels reflow instead of breaking. It finally looks like a proper dashboard rather than a wireframe.