Fix avatar upload username/email requirement issue (Issue #12)

- Remove duplicate onchange handler from avatar file input
- Prevent potential form submission conflicts between inline JS and event listener
- Avatar upload now properly uses only the JavaScript event listener with validation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

templates/settings_profile.html

@@ -258,7 +258,7 @@
                     <p>Upload a new profile picture to personalize your account</p>
                     <form id="upload-form" method="POST" action="{{ url_for('upload_avatar') }}" enctype="multipart/form-data">
                         <div class="file-upload">
-                            <input type="file" id="avatar" name="avatar" accept="image/*" onchange="this.form.submit()">
+                            <input type="file" id="avatar" name="avatar" accept="image/*">
                             <label for="avatar" class="file-upload-label">Choose New Picture</label>
                         </div>
                         <p class="help-text">PNG, JPG, or GIF. Maximum size 2MB.</p>