Removes 2-tab Groups/DMs layout; Chat screen is now DM-only for v1.0.
Groups tab state, rooms query, RoomCard/CreateRoomSheet imports removed.
Replaces static title+create-button header with sticky search field
(client-side filter on partnerName + lastMessage). No create-DM button
added — /dm-new route does not exist yet (follow-up task).
All #007AFF in chat.tsx replaced with colors.brandOrange.
Adds chat.search_placeholder to de/en/fr locales.
Tab-bar styles kept in makeStyles (dead code, v1.1 Groups comeback path).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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