Replace the docked right-aside AI chat with a floating, draggable,
resizable, minimizable window per the GitmostAgent design. The "AI chat"
entry points (page header menu, page-history item) now open the window
instead of the aside tab.
- Add ai-chat-window.tsx + ai-chat-window.module.css: fixed-position
window with viewport-clamped drag, CSS resize, minimize (hides body
via CSS so ChatThread/useChat stays mounted and streaming is not
aborted), and geometry kept in state (survives close/reopen, re-clamped
on open via useLayoutEffect, size tracked with a ResizeObserver).
- Reuse ChatThread, ConversationList and the transcript components
unchanged; move all orchestration (active chat, adopt-new-chat,
openPage, queries) into the window.
- Header shows a tokens-only badge: sum of persisted metadata.usage for
the active chat (no cost/context-total data available), hidden at 0.
- Add aiChatWindowOpenAtom; mount the window once in global-app-shell.
- Remove the aside "ai-chat" tab handling and delete ai-chat-panel.tsx.
- Type IAiChatMessageRow.metadata.usage; add "Minimize" and
"Tokens used in this chat" i18n keys.
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