Charts: timestamp x-axis, normalize mode, and explicit label control #8

Context

For a 6-month, 12-company market-cap chart I had to precompute everything outside the widget:

• No time axis. No DateTime/epoch input, so I formatted date strings, appended a synthetic "Now" point, forward-filled gaps across six exchanges' calendars, and passed one label per point.
• No label control. Labels needs one string per point; a shorter array labels only the leading points (verified with 5 labels over 100 points). LabelEvery / MaxLabels belongs in ChartOpts.
• Scale. With caps from $0.06T to $5.1T, the y-range flattens everything under the top three into indistinguishable lines. I built a second, percent-change series set to compare shapes.
• Gaps. Whether NaN breaks a line is undocumented; I forward-filled to be safe.

Proposal

new ChartOpts {
    XValues = epochs,                 // float[]
    TimeFormat = "MMM d",
    Normalize = Normalize.Index100,   // Index100 | Percent | None
    LabelEvery = 2,                   // or MaxLabels = 12
}

• Debug assert when Labels.Length is neither 0 nor the point count.
• Document NaN as the gap marker (or add explicit gap support).

Acceptance

The same chart can be written without app-side date formatting, date-union forward filling, or a second normalized series set.