feat: allow img in HTML identity signatures

- Restricts src to https: URLs or base64-embedded raster data: URIs (png/jpeg/gif/webp).
- SVG is excluded for safety reasons.
- Images with a disallowed src are removed entirely so they don't render as broken-image icons.

lib/__tests__/email-sanitization.test.ts

@@ -78,11 +78,67 @@ describe('email-sanitization', () => {
       expect(clean).toContain('John Doe');
     });
 
-    it('should remove images from signatures', () => {
-      const signature = '<p>John</p><img src="logo.png" alt="Logo">';
+    it('should allow img with https src', () => {
+      const signature = '<p>John</p><img src="https://cdn.example.com/logo.png" alt="Logo" width="120" height="40">';
       const clean = sanitizeSignatureHtml(signature);
+      expect(clean).toContain('<img');
+      expect(clean).toContain('src="https://cdn.example.com/logo.png"');
+      expect(clean).toContain('alt="Logo"');
+      expect(clean).toContain('width="120"');
+      expect(clean).toContain('height="40"');
+    });
+
+    it('should allow img with data:image/png;base64 src', () => {
+      const dataUri = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEX/AAAZ4gk3AAAAAXRSTlPM0jRW/QAAAAlwSFlzAAALEwAACxMBAJqcGAAAAA1JREFUCNdjYGBgAAAABAABc7Rs9wAAAABJRU5ErkJggg==';
+      const signature = `<img src="${dataUri}" alt="Logo">`;
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).toContain('<img');
+      expect(clean).toContain('data:image/png;base64,');
+    });
+
+    it('should allow img with data:image/jpeg, gif, webp', () => {
+      const cases = ['data:image/jpeg;base64,AAA', 'data:image/jpg;base64,AAA', 'data:image/gif;base64,AAA', 'data:image/webp;base64,AAA'];
+      for (const src of cases) {
+        const clean = sanitizeSignatureHtml(`<img src="${src}" alt="x">`);
+        expect(clean).toContain('<img');
+        expect(clean).toContain(src);
+      }
+    });
+
+    it('should strip img with http: src (https only)', () => {
+      const signature = '<img src="http://insecure.example.com/logo.png" alt="Logo">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('http://insecure.example.com');
       expect(clean).not.toContain('<img');
-      expect(clean).toContain('John');
+    });
+
+    it('should strip img with javascript: src', () => {
+      const signature = '<img src="javascript:alert(1)" alt="x">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('javascript:');
+      expect(clean).not.toContain('<img');
+    });
+
+    it('should strip img with data:image/svg+xml src (SVG forbidden)', () => {
+      const signature = '<img src="data:image/svg+xml;base64,PHN2Zy8+" alt="x">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('data:image/svg');
+      expect(clean).not.toContain('<img');
+    });
+
+    it('should strip img with non-image data: URI', () => {
+      const signature = '<img src="data:text/html;base64,PHA+aGk8L3A+" alt="x">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('data:text/html');
+      expect(clean).not.toContain('<img');
+    });
+
+    it('should strip event handlers on img', () => {
+      const signature = '<img src="https://cdn.example.com/logo.png" alt="x" onerror="alert(1)" onload="alert(2)">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('onerror');
+      expect(clean).not.toContain('onload');
+      expect(clean).toContain('https://cdn.example.com/logo.png');
     });
 
     it('should remove video and audio tags', () => {
@@ -113,16 +169,17 @@ describe('email-sanitization', () => {
     });
 
     it('should be stricter than email sanitization', () => {
-      const html = '<p>Text</p><img src="pic.jpg"><table><tr><td>Data</td></tr></table>';
+      const html = '<p>Text</p><table><tr><td>Data</td></tr></table><video src="v.mp4"></video>';
       const emailClean = sanitizeEmailHtml(html);
       const signatureClean = sanitizeSignatureHtml(html);
 
-      // Email allows img and table
-      expect(emailClean).toContain('<img');
+      // Email allows table
       expect(emailClean).toContain('<table>');
 
-      // Signature blocks img but may allow some tables (verify in implementation)
-      expect(signatureClean).not.toContain('<img');
+      // Signature blocks table and video
+      expect(signatureClean).not.toContain('<table');
+      expect(signatureClean).not.toContain('<video');
+      expect(signatureClean).toContain('Text');
     });
   });