refactor: decompose CareerConstellation monolith into focused modules

Break 1102-line CareerConstellation.tsx into:
- constellation/constants.ts: sizing, opacity, domain color tokens
- constellation/types.ts: SimNode, SimLink, LayoutParams interfaces
- hooks/useForceSimulation.ts: D3 simulation lifecycle
- hooks/useConstellationHighlight.ts: highlight/dim logic
- hooks/useConstellationInteraction.ts: mouse/touch/pin handlers
- constellation/MobileAccordion.tsx: tap-to-expand role details
- constellation/ConstellationLegend.tsx: domain legend
- constellation/AccessibleNodeOverlay.tsx: keyboard navigation buttons
- constellation/CareerConstellation.tsx: 288-line orchestrator

All existing behaviour preserved. Quality gates pass.

src/components/constellation/constants.ts

@@ -0,0 +1,30 @@
+// Sizing
+export const MIN_HEIGHT = 400
+export const MOBILE_FALLBACK_HEIGHT = 520
+export const ROLE_WIDTH = 104
+export const ROLE_HEIGHT = 32
+export const ROLE_RX = 16
+export const SKILL_RADIUS_DEFAULT = 7
+export const SKILL_RADIUS_ACTIVE = 11
+export const MOBILE_ROLE_WIDTH = 80
+export const MOBILE_SKILL_RADIUS_DEFAULT = 6
+export const MOBILE_SKILL_RADIUS_ACTIVE = 9
+export const MOBILE_LABEL_MAX_LEN = 10
+
+// Animation / opacity
+export const HIGHLIGHT_DIM_OPACITY = 0.15
+export const SKILL_REST_OPACITY = 0.35
+export const SKILL_ACTIVE_OPACITY = 0.9
+export const LINK_REST_OPACITY = 0.15
+export const LABEL_REST_OPACITY = 0.5
+
+// Domain color map
+export const DOMAIN_COLOR_MAP: Record<string, string> = {
+  clinical: '#059669',
+  technical: '#0D6E6E',
+  leadership: '#D97706',
+}
+
+// Media queries (evaluated once at module level)
+export const prefersReducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)').matches
+export const supportsCoarsePointer = window.matchMedia('(pointer: coarse)').matches