Fix chart bugs found on deployed site, redesign Chart 2 as box-and-whisker

Chart 4 (model predictions vs. observed) was picking the first row for a
given wave/model instead of summing across selected groups, so any district
whose first-returned group had zero counts (e.g. a suppressed race group)
showed a collapsed, flat modeled marker instead of the real aggregate
interval. Also fixes the rightmost wave label ("2021-22") clipping off the
edge of the small-multiple panels by anchoring edge ticks away from the
viewBox boundary instead of centering on it.

Chart 6's y-axis group labels (e.g. "American Indian / Alaska Native
Female") were wider than their margin and clipped past the left edge of the
SVG. Adds a shared shortGroupLabel() to colors.js and uses it here, matching
the convention already used in charts 2 and 5.

Chart 2 previously drew a plain bar to the modeled median next to an
observed diamond that often sat well past the bar's end, reading as if the
bar itself were an uncertainty range when it wasn't. Replaces it with an
actual horizontal box-and-whisker: whisker = the API's reported 90%
interval, box = the fitted approximation's 25th/75th percentiles (via a new
fit.quantile() inverse-CDF, exact round-trip of fitSkewedInterval's own
construction), median tick, observed diamond overlaid.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/charts/RateDensityRidgeline.jsx

@@ -1,5 +1,5 @@
 import { MODEL_QUADRANTS } from '../hooks/useApi.js'
-import { raceColor, OBSERVED_MARK_COLOR, RACE_LABELS } from '../utils/colors.js'
+import { raceColor, OBSERVED_MARK_COLOR, RACE_LABELS, SHORT_RACE_LABEL } from '../utils/colors.js'
 import { fitSkewedInterval, densityCurve } from '../utils/distributionApprox.js'
 import ChartLegend from '../components/ChartLegend.jsx'
 import ApproxNote from '../components/ApproxNote.jsx'
@@ -14,7 +14,6 @@ import ApproxNote from '../components/ApproxNote.jsx'
 
 const RACE_ORDER = ['WH', 'BL', 'HI', 'AM']
 const SEX_ORDER = ['F', 'M']
-const SHORT_RACE_LABEL = { WH: 'White', BL: 'Black', HI: 'Hispanic', AM: 'AI/AN' }
 
 function buildGroupRow(row) {
   const enroll = row.stu_enroll || 0