fix(inputs): cap room-name / display-name length client-side (H10)

The room-name (settings + create-room) and display-name inputs had no client-side
length guard, so an over-long value only failed after a server round-trip. Add
maxLength={255} (matching the existing inline-rename cap in RoomNavItem; under
Synapse's 256 max_displayname_length). Also clamp the emoji-picker prepend in the
two room-name fields, since programmatic setState isn't constrained by the DOM
maxLength and could otherwise push past the cap.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/settings/account/Profile.tsx

@@ -285,6 +285,7 @@ function ProfileDisplayName({ profile, userId }: ProfileProps) {
               onChange={handleChange}
               variant="Secondary"
               radii="300"
+              maxLength={255}
               style={{ paddingRight: config.space.S200 }}
               readOnly={changingDisplayName || disableSetDisplayname}
               after={