feat(F020): frontend infrastructure foundation

- src/lib/constants.ts: centralized route paths, labels, thresholds
- src/lib/utils.ts: formatting, color helpers, math utils
- src/hooks/: useProperties, useMatches, useFutureSignals, useNeeds
- src/components/scores/MatchScoreRing
- src/components/data-quality/DataQualityBar
- src/components/future-signals/SignalTypeBadge
- src/components/cards/SourceTypeBadge
- src/provider/AuthProvider (placeholder, swappable)
- main.tsx: AuthProvider + centralized stale time

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/provider/AuthProvider.tsx

@@ -0,0 +1,36 @@
+import { createContext, useContext, type ReactNode } from 'react'
+import { useSessionStore } from '../stores/sessionStore'
+import type { MockUser } from '../stores/sessionStore'
+
+// Placeholder AuthContext — swap for real auth (Supabase, Auth0, etc.) later.
+// All call sites use this context; no component imports sessionStore directly.
+
+interface AuthContextValue {
+  user: MockUser | null
+  isAuthenticated: boolean
+  isLoading: boolean
+  login: (user: MockUser) => void
+  logout: () => void
+}
+
+const AuthContext = createContext<AuthContextValue | null>(null)
+
+export function AuthProvider({ children }: { children: ReactNode }) {
+  const { currentUser, isAuthenticated, login, logout } = useSessionStore()
+
+  const value: AuthContextValue = {
+    user: currentUser,
+    isAuthenticated,
+    isLoading: false, // always resolved in mock mode
+    login,
+    logout,
+  }
+
+  return <AuthContext.Provider value={value}>{children}</AuthContext.Provider>
+}
+
+export function useAuth(): AuthContextValue {
+  const ctx = useContext(AuthContext)
+  if (!ctx) throw new Error('useAuth must be used within AuthProvider')
+  return ctx
+}