Replace regular double-centering (/n) with Székely & Rizzo 2014
U-centering (/(n-2)) in bcCenter, clamp dCor² to 0 with Math.max
instead of Math.abs, raise guard from m<3 to m<4 since the
1/(n*(n-3)) factor is undefined at n=3, and update the V-shape
test to use n=15 where U-centering produces positive dCovXY.

- Updated test name from '< 3 complete pairs' to '< 4 complete pairs'
- Added missing n=3 test case to the boundary check (1/(m*(m-3)) undefined)
- Fixed comment in distanceCorr function to reflect n<4 boundary

Co-Authored-By: fahimfaisaal <[email protected]>

…o computeCorrelation

…method

…nce options

…section

Zero-valued measurements were silently omitted from JSON output because the
old float64 field used omitempty. *float64 + F64() lets callers explicitly
encode zero while nil still serialises as absent.

…lone

- Add StatConfig.StatEnabled/StatMath methods as single source of truth
- Add MaterialiseStatFlags to build *StatConfig from flag slice (nil = omit)
- Add ChartConfigNeedsCorrelation shared predicate
- Fix AggregateDataPoints: treat nil Value as 0 not skip (data loss bug)
- Fix deepCloneData: deep-copy *float64 pointers to avoid shared mutation

…ateUI

Ships the heatmap echarts module even when heatmap is not a visible chart
tab, so StatsPanel correlation renderer works regardless of chart selection.

…Stat field

Extends ChartConfig interface with StatEnabled/StatMath. All five chart
configs carry a *StatConfig field and delegate to StatConfig methods so
logic lives in one place. Materialise uses shared.MaterialiseStatFlags
so absent --stat produces nil (omitted from JSON) not a zero-value struct.

Each chart subcommand's RunE now reads stat flags from the cobra config
registry and passes them to Materialise, which calls MaterialiseStatFlags
once. Removes the per-chart inline stat-block duplication.

- RewriteStatArg: skip consuming next arg if it resolves to a real file
- validateStat: replace hand-rolled fatal validation with ApplyValidationRules
- settingsNeedCorrelation / anyDatasetNeedsCorrelation: use shared predicate
- applyStatToSettings: add exhaustive default panic
- options: add 'confidence' to --stat help text (was missing from both strings)

- ChartCard: hasStats checks stat.enabled===true (not !=false) so legacy
  files without a stat field never show the Stats button
- StatsPanel / stats.worker: correlation method picker and adaptive scale
- chartConfig / common: stat-aware series and axis config helpers
- bar/line/pie/radar chart options: consume stat math for category gating