- Vg/Rg/RL inputs in a single horizontal row
- Segments and signal shape panels placed side by side below
- Time scale slider moved to left (segments) column
- Math/computed values section moved to bottom of page below plots
- Bump font sizes across UI (labels 12→14px, cfg-row 13→15px, etc.)
- Page title shortened to "Transmission line visualizer"

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

The centered erf (50% at wavefront arrival) was non-causal with a visible
precursor ahead of the front. Replace with shifted erf:
0.5*(1+erf(k*(2*dt/tr-1))), clamped to 0/1 outside [0, tr].

Both rise shapes (linear ramp and erf S-curve) now share the same tr
parameter and are strictly causal. Unify model.riseTimeTau/riseTimeTr
into model.riseTimeTr + model.riseShape ("step"|"linear"|"erf").

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

The first-order RC exponential (1-exp(-dt/tau)) had infinite slope at
dt=0 and a lazy asymptotic tail — not physically realistic. Replace with
0.5*(1+erf(dt/tau)), which models skin-effect losses (alpha proportional
to sqrt(f)) and gives zero slope at dt=0 with a smooth symmetric sigmoid.

- Add erf() rational approximation (Abramowitz & Stegun 7.1.26)
- Extend waveVoltageAt spatial window by 3*tau for precursor foot
- Update sumEventsWithRise to include events up to 3*tau ahead
- Rename UI option to "Gaussian rise (skin-effect)"

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