[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/features/annotations/AnnotationsPage.tsx

@@ -1,11 +1,11 @@
 import { useState, useCallback, useEffect, useRef } from 'react'
-import { useResizablePanel } from '../../hooks/useResizablePanel'
-import { api } from '../../api/client'
+import { useResizablePanel } from '../../hooks'
+import { api } from '../../api'
 import MediaList from './MediaList'
 import VideoPlayer, { type VideoPlayerHandle } from './VideoPlayer'
 import CanvasEditor, { type CanvasEditorHandle } from './CanvasEditor'
 import AnnotationsSidebar from './AnnotationsSidebar'
-import DetectionClasses from '../../components/DetectionClasses'
+import { DetectionClasses } from '../../components'
 import { AnnotationSource, AnnotationStatus, MediaType } from '../../types'
 import { getClassColor, getClassNameFallback, getPhotoModeSuffix } from './classColors'
 import type { Media, AnnotationListItem, Detection } from '../../types'

src/features/annotations/AnnotationsSidebar.tsx

@@ -1,8 +1,7 @@
 import { useEffect, useState } from 'react'
 import { useTranslation } from 'react-i18next'
 import { FaDownload } from 'react-icons/fa'
-import { api } from '../../api/client'
-import { createSSE } from '../../api/sse'
+import { api, createSSE } from '../../api'
 import { getClassColor } from './classColors'
 import type { Media, AnnotationListItem, PaginatedResponse } from '../../types'
 

src/features/annotations/MediaList.tsx

@@ -1,10 +1,9 @@
 import { useState, useEffect, useCallback, useRef } from 'react'
 import { useTranslation } from 'react-i18next'
 import { useDropzone } from 'react-dropzone'
-import { useFlight } from '../../components/FlightContext'
-import { api } from '../../api/client'
-import { useDebounce } from '../../hooks/useDebounce'
-import ConfirmDialog from '../../components/ConfirmDialog'
+import { useFlight, ConfirmDialog } from '../../components'
+import { api } from '../../api'
+import { useDebounce } from '../../hooks'
 import { MediaType } from '../../types'
 import type { Media, PaginatedResponse, AnnotationListItem } from '../../types'
 

src/features/annotations/index.ts

@@ -0,0 +1,12 @@
+export { default as AnnotationsPage } from './AnnotationsPage'
+// CanvasEditor remains in the Public API while F2 (cross-feature edge to
+// 07_dataset) is open. Closing F2 will remove this re-export.
+export { default as CanvasEditor } from './CanvasEditor'
+//
+// classColors symbols are NOT re-exported here. The file is logically owned
+// by 11_class-colors but lives under this directory until F3 moves it. Re-
+// exporting through this barrel creates a circular dependency
+//   AnnotationsPage -> DetectionClasses -> 06_annotations barrel -> AnnotationsPage
+// because DetectionClasses (03_shared-ui) imports classColors. Consumers
+// import classColors directly via `src/features/annotations/classColors`
+// as a documented F3-pending exemption. STC-ARCH-01 carries the exemption.