feat: add character avatars with upload and zoom functionality

- Add avatar upload with file picker dialog
- Display avatars in header, chat messages, and settings
- Implement clickable avatars with full-screen zoom modal
- Enable asset protocol for local file access in Tauri config
- Add tauri-plugin-dialog for native file selection
- Store avatars in ~/.config/claudia/avatars/
- Support PNG, JPG, JPEG, and WEBP formats
- Modal closes on overlay click or ESC key

src/styles.css

@@ -84,6 +84,28 @@ body {
   border-radius: 50%;
   background: var(--bg-tertiary);
   border: 1px solid var(--border);
+  background-size: cover;
+  background-position: center;
+}
+
+.avatar-circle-large {
+  width: 80px;
+  height: 80px;
+  border-radius: 50%;
+  background: var(--bg-tertiary);
+  border: 2px solid var(--border);
+  background-size: cover;
+  background-position: center;
+}
+
+.avatar-upload {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+}
+
+.avatar-preview {
+  flex-shrink: 0;
 }
 
 #character-header-name {
@@ -730,6 +752,65 @@ body {
   border: 1px solid rgba(239, 68, 68, 0.2);
 }
 
+/* Avatar Modal */
+.avatar-modal {
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  z-index: 10000;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.avatar-modal-overlay {
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  background: rgba(0, 0, 0, 0.85);
+  backdrop-filter: blur(8px);
+  -webkit-backdrop-filter: blur(8px);
+  cursor: pointer;
+}
+
+.avatar-modal-content {
+  position: relative;
+  z-index: 1;
+  max-width: 90vw;
+  max-height: 90vh;
+  pointer-events: none;
+}
+
+.avatar-modal-content img {
+  max-width: 100%;
+  max-height: 90vh;
+  border-radius: 12px;
+  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
+  object-fit: contain;
+}
+
+/* Make avatars clickable */
+.avatar-circle,
+.avatar-circle-large {
+  cursor: pointer;
+  transition: transform 0.2s ease, box-shadow 0.2s ease;
+}
+
+.avatar-circle:hover,
+.avatar-circle-large:hover {
+  transform: scale(1.05);
+  box-shadow: 0 4px 12px rgba(99, 102, 241, 0.3);
+}
+
+.avatar-circle:active,
+.avatar-circle-large:active {
+  transform: scale(0.95);
+}
+
 /* Responsive */
 @media (max-width: 600px) {
   .messages-list {