Let chart views avoid the dashboard utility bulk

The intraday chart data builder lived inside dashboard-utils with observation-source and TAF helpers, so chart consumers had to depend on the large dashboard utility surface. This moves chart data preparation, observation-source helpers, and TAF marker labels into focused modules while keeping dashboard-utils re-export compatibility.

Constraint: Preserve existing chart data shape, observation labels, TAF labels, and legacy dashboard-utils exports.

Rejected: Rewrite chart data generation while moving it | this pass is a boundary move only so visual behavior remains stable.

Confidence: high

Scope-risk: moderate

Reversibility: clean

Tested: TypeScript diagnostics for chart-utils, dashboard-utils, observation-source-utils, and taf-utils

Tested: npm run build

Not-tested: Browser visual regression across every chart city.

frontend/components/dashboard/FutureForecastModal.tsx

@@ -23,11 +23,11 @@ import {
   ModelForecast,
   ProbabilityDistribution,
 } from "@/components/dashboard/PanelSections";
+import { getTemperatureChartData } from "@/lib/chart-utils";
 import {
   getFutureModalView,
   getModelView,
   getProbabilityView,
-  getTemperatureChartData,
   getWeatherSummary,
 } from "@/lib/dashboard-utils";
 import { getTodayPaceView } from "@/lib/pace-utils";