feat: add camera capture component (refs #66)

Implements a reusable React camera capture component with:
- getUserMedia API for camera access on mobile and desktop
- Translucent aspect-ratio guidance overlays (VIN ~6:1, receipt ~2:3)
- Post-capture crop tool with draggable handles
- File input fallback for desktop and unsupported browsers
- Support for HEIC, JPEG, PNG (sent as-is to server)
- Full mobile responsiveness (320px - 1920px)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/shared/CLAUDE.md

@@ -0,0 +1,32 @@
+# frontend/src/shared/
+
+Shared components that are reusable across multiple features.
+
+## Subdirectories
+
+| Directory | What | When to read |
+| --------- | ---- | ------------ |
+| `components/CameraCapture/` | Camera capture with crop tool | Building OCR features, image upload |
+
+## Components
+
+### CameraCapture
+
+Full-featured camera capture component with:
+- `getUserMedia` API for camera access
+- Translucent guidance overlays (VIN, receipt, document)
+- Post-capture crop tool
+- File input fallback for desktop/unsupported browsers
+- HEIC, JPEG, PNG support
+
+Usage:
+```tsx
+import { CameraCapture } from '@/shared/components/CameraCapture';
+
+<CameraCapture
+  onCapture={(file, croppedFile) => handleCapture(file, croppedFile)}
+  onCancel={() => setShowCamera(false)}
+  guidanceType="vin"
+  allowCrop={true}
+/>
+```