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/components/layout/ActivityPanel.tsx

@@ -33,6 +33,9 @@ export function ActivityPanel() {
         username: friend.username,
         displayName: friend.displayName,
         avatar: friend.avatar,
+        banner: friend.banner,
+        accentColor: friend.accentColor,
+        bio: friend.bio,
         status: friend.status,
         customStatus: friend.customStatus,
         createdAt: friend.createdAt,

packages/web/src/components/layout/AppLayout.tsx

@@ -15,6 +15,7 @@ import { SpaceSettingsModal } from '../modals/SpaceSettings';
 import { ChannelSettingsModal } from '../modals/ChannelSettingsModal';
 import { NewDmModal } from '../modals/NewDmModal';
 import { AddDmMemberModal } from '../modals/AddDmMemberModal';
+import { UserProfileModal } from '../modals/UserProfileModal';
 import { IncomingCallModal } from '../voice/IncomingCallModal';
 import { PictureInPicture } from '../voice/PictureInPicture';
 import { SoundController } from '../voice/SoundController';
@@ -276,6 +277,7 @@ export function AppLayout() {
       <ChannelSettingsModal />
       <NewDmModal />
       <AddDmMemberModal />
+      <UserProfileModal />
       <IncomingCallModal />
       <ImagePreview />
       <PictureInPicture />