feat(frontend): public channels, self-excluded member picker, editable display name

- create-channel modal: Public checkbox (default off), self excluded from
  member list (creator auto-added), shows member display names
- Settings modal to edit your own display name
- members panel shows names and marks (you)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/auth/AuthContext.tsx

@@ -2,7 +2,7 @@ import { useMemo, useState } from 'react'
 import type { PropsWithChildren } from 'react'
 import { clearAuthSession, getAuthSession, isAccessTokenStale, setAuthSession } from '../lib/auth-storage'
 import type { AuthSession } from '../lib/auth-storage'
-import { loginCenter, logoutCenter, meGuildsCenter, refreshCenter } from '../lib/center-auth-client'
+import { loginCenter, logoutCenter, meGuildsCenter, refreshCenter, updateMeNameCenter } from '../lib/center-auth-client'
 import { AuthContext } from './auth-context'
 import type { AuthContextValue } from './auth-context'
 
@@ -72,6 +72,22 @@ export function AuthProvider({ children }: PropsWithChildren) {
         setAuthSession(next)
         setSession(next)
       },
+      updateName: async (name: string) => {
+        if (!session) return
+        const accessToken = (await (async () => {
+          if (!isAccessTokenStale(session.accessToken)) return session.accessToken
+          const refreshed = await refreshCenter(session.centerApiBase, session.refreshToken)
+          return refreshed.accessToken
+        })())
+        const updated = await updateMeNameCenter(session.centerApiBase, accessToken, name)
+        const next: AuthSession = {
+          ...session,
+          accessToken,
+          user: { ...session.user, name: updated.name },
+        }
+        setAuthSession(next)
+        setSession(next)
+      },
     }),
     [session],
   )