fix(20): IN-02 add maxLength to display-name and username inputs

Add maxLength={256} to the edit-mode and create-mode display-name inputs,
and maxLength={128} to the create-mode username input, matching the server-
side Zod schema limits. This surfaces the constraint client-side instead of
letting a long entry reach the server and return a generic 400.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/pwa/src/components/MemberEditorSheet.tsx

@@ -497,6 +497,7 @@ export function MemberEditorSheet({
                 <input
                   id="editor-display-name"
                   type="text"
+                  maxLength={256}
                   value={displayName}
                   onChange={(e) => setDisplayName(e.target.value)}
                   aria-describedby={profileError ? 'profile-error' : undefined}
@@ -822,6 +823,7 @@ export function MemberEditorSheet({
               <input
                 id="create-display-name"
                 type="text"
+                maxLength={256}
                 value={createDisplayName}
                 onChange={(e) => setCreateDisplayName(e.target.value)}
                 aria-describedby={createError ? 'create-error' : undefined}
@@ -837,6 +839,7 @@ export function MemberEditorSheet({
               <input
                 id="create-username"
                 type="text"
+                maxLength={128}
                 autoComplete="off"
                 spellCheck={false}
                 autoCapitalize="none"