Refactor/zustand slices chat store

[sudorishabh]

refactor(react): consolidate Zustand stores via chat layout/data/auth stores

Why

The React package had many tiny Zustand stores (often a single boolean + setter). This increased import churn and made cross-panel logic harder to maintain. Consolidating into slice-like stores reduces fragmentation and simplifies “exclusive panel open” behavior.

Summary

• Consolidated fragmented Zustand “panel visibility” state into useChatLayoutStore (openExclusivePanel) and migrated all sidebar/panel consumers.
• Consolidated starred message data into useChatDataStore; removed starredMessageStore.
• Consolidated login/TOTP modal/loading state into useAuthStore; removed loginStore and totpmodalStore.
• Removed legacy useSetExclusiveState hook; updated all call sites (including @embeddedchat/markups UserMention).

Fixes #1282

Key changes

• New stores
  • packages/react/src/store/chatLayoutStore.js
  • packages/react/src/store/chatDataStore.js
  • packages/react/src/store/authStore.js
• Deleted fragmented stores
  • packages/react/src/store/sidebarStore.js
  • packages/react/src/store/pinnedMessageStore.js
  • packages/react/src/store/searchMessageStore.js
  • packages/react/src/store/fileStore.js
  • packages/react/src/store/mentionsStore.js
  • packages/react/src/store/threadsMessageStore.js
  • packages/react/src/store/starredMessageStore.js
  • packages/react/src/store/loginStore.js
  • packages/react/src/store/totpmodalStore.js
  • packages/react/src/hooks/useSetExclusiveState.js

Test plan

• Run Storybook and verify sidebar panels:
  • Open each panel from the header menu (Members/Search/Room Info/Threads/Files/Mentions/Pinned/Starred/User Info) and confirm it closes the others.
  • Close panels via the sidebar close button.
• Verify auth flow:
  • Open login modal, submit invalid credentials (error toast).
  • Trigger TOTP-required flow (login modal closes, TOTP modal opens).
• Verify starred messages:
  • Open Starred panel and confirm list renders after fetch.

Notes

• yarn lint failures seen locally are due to pre-existing Prettier CRLF (Delete ␍) issues in unrelated files; not introduced by this PR.
• Similar store fragmentation still exists in other packages (react-native, layout_editor) and can be refactored separately.

PR Test Details

Note: The PR will be ready for live testing at https://rocketchat.github.io/EmbeddedChat/pulls/pr-1283
after approval.