feat: user profile customization with banner, accent color, bio, and full profile modal

Add banner image, accent color, and bio fields to user profiles with
full-stack support: schema migration, API validation (hex color format,
190-char bio limit), sanitizeUser propagation, and new GET /users/:id/mutuals
endpoint. Rewrite AccountPanel with live preview card, avatar/banner upload
via ImageCropModal, 16-preset accent color picker, and bio editor. Enhance
UserProfilePopout with banner display, accent-colored names, bio rendering,
and mutual counts. Add new UserProfileModal with About/Mutual Friends/Mutual
Spaces tabs and friend action buttons.

packages/web/src/stores/authStore.ts

@@ -16,7 +16,7 @@ interface AuthState {
   register: (username: string, password: string, displayName?: string) => Promise<void>;
   logout: () => void;
   loadUser: () => Promise<void>;
-  updateProfile: (data: { displayName?: string; avatar?: string; customStatus?: string; status?: UserStatus }) => Promise<void>;
+  updateProfile: (data: { displayName?: string; avatar?: string; banner?: string; accentColor?: string; bio?: string; customStatus?: string; status?: UserStatus }) => Promise<void>;
   setUser: (user: User) => void;
   clearError: () => void;
 }

packages/web/src/stores/uiStore.ts

@@ -13,6 +13,7 @@ type ModalType =
   | 'imagePreview'
   | 'newDm'
   | 'addDmMember'
+  | 'userProfile'
   | null;
 
 interface Toast {