refactor: consolidate AI analyzers into shared lib/ai module and add journal entry reversal columns

Extract shared vision/document analysis logic into lib/ai (vision-client, document-analyzer,
image preprocessing, validation helpers), simplifying invoice-analyzer, receipt-analyzer, and
document classifier. Add migration 046 for journal entry reversal/correction link columns
(reversed_by_id, reverses_id, correction_of_id) required by storno service. Update extension
components and shared UI.

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

lib/ai/__tests__/preprocess-image.test.ts

@@ -0,0 +1,68 @@
+import { describe, it, expect, vi } from 'vitest'
+
+// Mock server-only
+vi.mock('server-only', () => ({}))
+
+// Mock sharp - use vi.hoisted to avoid initialization order issues
+const { mockSharp, mockSharpChain, mockToBuffer } = vi.hoisted(() => {
+  const mockToBuffer = vi.fn()
+  const mockSharpChain = {
+    grayscale: vi.fn().mockReturnThis(),
+    normalize: vi.fn().mockReturnThis(),
+    sharpen: vi.fn().mockReturnThis(),
+    jpeg: vi.fn().mockReturnThis(),
+    toBuffer: mockToBuffer,
+  }
+  const mockSharp = vi.fn().mockReturnValue(mockSharpChain)
+  return { mockSharp, mockSharpChain, mockToBuffer }
+})
+
+vi.mock('sharp', () => ({ default: mockSharp }))
+
+import { preprocessImage } from '../preprocess-image'
+
+describe('preprocessImage', () => {
+  it('returns PDFs unchanged', async () => {
+    const result = await preprocessImage('pdf-base64-data', 'application/pdf')
+
+    expect(result.base64).toBe('pdf-base64-data')
+    expect(result.mimeType).toBe('application/pdf')
+    expect(mockSharp).not.toHaveBeenCalled()
+  })
+
+  it('processes JPEG images through sharp pipeline', async () => {
+    const inputBase64 = Buffer.from('fake-image-data').toString('base64')
+    const outputBuffer = Buffer.from('processed-image')
+    mockToBuffer.mockResolvedValueOnce(outputBuffer)
+
+    const result = await preprocessImage(inputBase64, 'image/jpeg')
+
+    expect(mockSharp).toHaveBeenCalled()
+    expect(mockSharpChain.grayscale).toHaveBeenCalled()
+    expect(mockSharpChain.normalize).toHaveBeenCalled()
+    expect(mockSharpChain.sharpen).toHaveBeenCalledWith({ sigma: 1.5 })
+    expect(mockSharpChain.jpeg).toHaveBeenCalledWith({ quality: 90 })
+    expect(result.mimeType).toBe('image/jpeg')
+    expect(result.base64).toBe(outputBuffer.toString('base64'))
+  })
+
+  it('processes PNG images and outputs as JPEG', async () => {
+    const inputBase64 = Buffer.from('fake-png-data').toString('base64')
+    const outputBuffer = Buffer.from('processed-png')
+    mockToBuffer.mockResolvedValueOnce(outputBuffer)
+
+    const result = await preprocessImage(inputBase64, 'image/png')
+
+    expect(result.mimeType).toBe('image/jpeg')
+    expect(mockSharp).toHaveBeenCalled()
+  })
+
+  it('processes WebP images', async () => {
+    const inputBase64 = Buffer.from('fake-webp').toString('base64')
+    mockToBuffer.mockResolvedValueOnce(Buffer.from('out'))
+
+    const result = await preprocessImage(inputBase64, 'image/webp')
+
+    expect(result.mimeType).toBe('image/jpeg')
+  })
+})