[AZ-485] Add Public API barrels + STC-ARCH-01 (F4 close)

Closes architecture baseline finding F4. Every component now exposes
its Public API through `src/<component>/index.ts`; cross-component
imports go through the barrel. `scripts/check-arch-imports.mjs` plus
`STC-ARCH-01` in the static profile enforce the rule; tests in
`tests/architecture_imports.test.ts` cover AC-4/AC-5 + 2 exemption
cases. One F3-pending exemption (`classColors`) is documented in 5
places (barrel, consumer, script, doc, test) to avoid a circular
import.

Phase B cycle 1 batch 1 of 2 (epic AZ-447). Batch 2 is AZ-486
(endpoint builders) — blocked on this commit landing.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/components/DetectionClasses.tsx

@@ -2,7 +2,11 @@ import { useEffect, useState } from 'react'
 import { useTranslation } from 'react-i18next'
 import { MdOutlineWbSunny, MdOutlineNightlightRound } from 'react-icons/md'
 import { FaRegSnowflake } from 'react-icons/fa'
-import { api } from '../api/client'
+import { api } from '../api'
+// classColors lives under 06_annotations until F3 moves it to its own home.
+// Importing through the 06_annotations barrel would create a cycle
+// (DetectionClasses -> 06_annotations barrel -> AnnotationsPage -> DetectionClasses).
+// STC-ARCH-01 exempts this single path as an F3-pending edge.
 import { getClassColor, FALLBACK_CLASS_NAMES } from '../features/annotations/classColors'
 import type { DetectionClass } from '../types'
 

src/components/FlightContext.tsx

@@ -1,5 +1,5 @@
 import { createContext, useContext, useState, useEffect, useCallback, type ReactNode } from 'react'
-import { api } from '../api/client'
+import { api } from '../api'
 import type { Flight, UserSettings } from '../types'
 
 interface FlightState {

src/components/Header.tsx

@@ -1,6 +1,6 @@
 import { NavLink, useNavigate } from 'react-router-dom'
 import { useTranslation } from 'react-i18next'
-import { useAuth } from '../auth/AuthContext'
+import { useAuth } from '../auth'
 import { useFlight } from './FlightContext'
 import { useState, useRef, useEffect } from 'react'
 import HelpModal from './HelpModal'

src/components/index.ts

@@ -0,0 +1,5 @@
+export { default as Header } from './Header'
+export { default as HelpModal } from './HelpModal'
+export { default as ConfirmDialog } from './ConfirmDialog'
+export { default as DetectionClasses } from './DetectionClasses'
+export { FlightProvider, useFlight } from './FlightContext'