feat: dashboard analytics and interaction telemetry (issue #15)

[WFord26]

Summary

Implements structured analytics telemetry for key dashboard interactions as described in issue #15.

Changes

hooks/useAnalytics.ts

Added useDashboardTelemetry() hook with stable callbacks for all instrumented events:

Callback	Event Name	Description
trackFilterChanged	dashboard_filter_changed	Any filter change (fuel type, region, etc.)
trackTimeRangeChanged	time_range_changed	Historical chart time range selector
trackStateDrilldown	state_drilldown_opened	Map state click → state page
trackChartAnnotationOpened	chart_annotation_opened	Event annotation marker click
trackStoryCardOpened	story_card_opened	Market story card actioned
trackCompareModeEnabled	compare_mode_enabled	Compare mode activated (ready for future UI)
trackPanelExpanded	panel_expanded	Collapsible panel opened (ready for future UI)

pages/Dashboard.tsx

• Fuel type toggle buttons emit dashboard_filter_changed with previous value
• Map onStateClick emits state_drilldown_opened with state abbr + fuel type
• Story card onAction emits story_card_opened with card id, title, and category

pages/Historical.tsx

• Time range buttons emit time_range_changed with previous range
• Chart event reference lines carry id/category metadata and emit chart_annotation_opened on click

components/charts/PriceLineChart.tsx

• Extended ChartReferenceLine with id and category fields
• Added optional onAnnotationClick prop to enable clickable annotation markers

test/useAnalytics.test.ts

12 tests covering all event shapes, optional fields, and callback stability.

Acceptance Criteria

• Key dashboard interactions emit structured analytics events
• Event names and payloads are documented and consistent
• Instrumentation covers public dashboard adoption beyond page views

Closes #15