Restructure chat service, web routes, and add test suite

Split monolithic chat service into modular structure with Matrix client
support, extract web server into per-resource route modules, introduce
bootstrap/main-loop separation, and add comprehensive vitest coverage
across services, repositories, and utilities. Adds project docs and
CLAUDE.md agent instructions.

tests/image-utils.test.ts

@@ -0,0 +1,74 @@
+import { describe, it, expect } from 'vitest';
+import { isValidImageMimeType, bufferToBase64 } from '../src/utils/image.js';
+
+describe('isValidImageMimeType', () => {
+  it('accepts valid image MIME types', () => {
+    expect(isValidImageMimeType('image/jpeg')).toBe(true);
+    expect(isValidImageMimeType('image/png')).toBe(true);
+    expect(isValidImageMimeType('image/gif')).toBe(true);
+    expect(isValidImageMimeType('image/webp')).toBe(true);
+  });
+
+  it('rejects invalid MIME types', () => {
+    expect(isValidImageMimeType('text/plain')).toBe(false);
+    expect(isValidImageMimeType('application/pdf')).toBe(false);
+    expect(isValidImageMimeType('video/mp4')).toBe(false);
+    expect(isValidImageMimeType('application/json')).toBe(false);
+    expect(isValidImageMimeType('text/html')).toBe(false);
+  });
+
+  it('rejects empty string', () => {
+    expect(isValidImageMimeType('')).toBe(false);
+  });
+
+  it('rejects null-like values', () => {
+    expect(isValidImageMimeType('null' as unknown as string)).toBe(false);
+    expect(isValidImageMimeType('undefined' as unknown as string)).toBe(false);
+  });
+
+  it('is case-sensitive (lowercase required)', () => {
+    // The function checks exact matches against lowercase values
+    expect(isValidImageMimeType('IMAGE/JPEG')).toBe(false);
+    expect(isValidImageMimeType('Image/Png')).toBe(false);
+  });
+
+  it('rejects MIME types with parameters', () => {
+    expect(isValidImageMimeType('image/jpeg; charset=utf-8')).toBe(false);
+    expect(isValidImageMimeType('image/png; alpha')).toBe(false);
+  });
+});
+
+describe('bufferToBase64', () => {
+  it('converts buffer to base64 string', () => {
+    const buffer = Buffer.from('hello world');
+    const result = bufferToBase64(buffer);
+    expect(result).toBe(btoa('hello world'));
+  });
+
+  it('handles empty buffer', () => {
+    const buffer = Buffer.from('');
+    const result = bufferToBase64(buffer);
+    expect(result).toBe('');
+  });
+
+  it('handles binary data', () => {
+    const buffer = Buffer.from([0x00, 0x01, 0x02, 0xff, 0xfe, 0xfd]);
+    const result = bufferToBase64(buffer);
+    expect(result).toBe(btoa('\x00\x01\x02\xff\xfe\xfd'));
+  });
+
+  it('handles large buffer', () => {
+    const buffer = Buffer.alloc(1024 * 1024); // 1MB
+    buffer.fill(0x41); // 'A'
+    const result = bufferToBase64(buffer);
+    expect(result.length).toBeGreaterThan(0);
+    // Base64 encodes each 3 bytes as 4 chars, rounding up.
+    expect(result.length).toBe(Math.ceil((1024 * 1024) / 3) * 4);
+  });
+
+  it('produces valid base64 (only valid chars)', () => {
+    const buffer = Buffer.from(Math.random().toString(36).repeat(100));
+    const result = bufferToBase64(buffer);
+    expect(result).toMatch(/^[A-Za-z0-9+/]+=*$/);
+  });
+});