Fix EquilibriumPlot crash on empty/sparse data

[meganrm]

Problem

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EquilibriumPlot crashed / produced NaN garbage when fewer than 3 equilibrium points had been recorded. Math.max(...x) and the bestFit regression (regression.logarithmic/regression.exponential) ran unconditionally, before the component's own bestFitVisible = x.length >= 3 guard — which only gated display, not the computation itself.

Fixes #225

Solution

Guarded the bestFit useMemo and the standalone Math.max(...x) with the same x.length >= 3 threshold already used elsewhere in the component, short-circuiting to a safe default ({ x: [], y: [], value: NaN }) when there isn't enough data. No behavior change for 3+ points — the plot already correctly hid the best-fit line/indicator below 3 points, this just stops the underlying computation from crashing on the way there.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Change summary:

• Guard bestFit regression against empty/too-few data points
• Guard standalone Math.max(...x) the same way
• Guard tickvals so it doesn't push NaN when the best-fit line isn't visible

Steps to Verify:

1. Start a High Affinity, Low Affinity, or Competitive Binding experiment
2. Before recording any equilibrium points, confirm the plot renders without error
3. Record 1-2 points — confirm no crash, no best-fit line (unchanged from prior behavior)
4. Record 3+ points — confirm the best-fit line / Kd or Ki indicator still renders correctly, unchanged from before

Screenshots (optional):

Keyfiles (delete if not relevant):

1. src/components/plots/EquilibriumPlot.tsx

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