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/api/client.ts

@@ -45,6 +45,7 @@ export class BackspaceApiClient {
     update: (data: UpdateUserRequest) => Promise<User>;
     get: (id: string) => Promise<User>;
     verifyPassword: (password: string) => Promise<VerifyPasswordResponse>;
+    getMutuals: (id: string) => Promise<{ mutualFriends: User[]; mutualSpaces: { id: string; name: string; icon: string | null }[] }>;
   };
 
   readonly spaces: {
@@ -210,6 +211,8 @@ export class BackspaceApiClient {
       get: (id: string) => request<User>('GET', `/users/${id}`),
       verifyPassword: (password: string) =>
         request<VerifyPasswordResponse>('POST', '/users/@me/verify-password', { password }),
+      getMutuals: (id: string) =>
+        request<{ mutualFriends: User[]; mutualSpaces: { id: string; name: string; icon: string | null }[] }>('GET', `/users/${id}/mutuals`),
     };
 
     this.spaces = {