Add synthetic array (waveform) DSP support + UX improvements

Adds full array/waveform support through the synthetic DSP engine: a
dsp.Sample value model (scalar or []float64), array ops (index, slice,
sum, mean, min, max, length, fft) with an in-tree radix-2 FFT, and static
type propagation (OpOutputType) that the editor mirrors to colour wires by
data type and flag invalid wirings. Stateful filters and lua stay
scalar-only. Adds a waveform plot mode (x-vs-index trace).

Also: errored-node hover reasons, S/N add-signal/add-node HUD shortcuts in
the synthetic editor, and view-mode widgets that blend with the canvas
background (chrome kept in edit mode).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/PropertiesPane.tsx

@@ -302,6 +302,7 @@ export default function PropertiesPane({ selected, multiCount, iface, onChange,
                       <option value="fft">FFT</option>
                       <option value="waterfall">Waterfall</option>
                       <option value="logic">Logic analyser</option>
+                      <option value="waveform">Waveform (array)</option>
                     </select>
                   </Field>
                   {(w.options['plotType'] ?? 'timeseries') === 'timeseries' && (