refactor(components): reorganize onboarding/provider auth/sidebar indicator into domain features

- Move onboarding out of root-level components into a dedicated feature module:
  - add src/components/onboarding/view/Onboarding.tsx
  - split onboarding UI into focused subcomponents:
    - OnboardingStepProgress
    - GitConfigurationStep
    - AgentConnectionsStep
    - AgentConnectionCard
  - add onboarding-local types and utils for provider status and validation helpers

- Move multi-provider login modal into a dedicated provider-auth feature:
  - add src/components/provider-auth/view/ProviderLoginModal.tsx
  - add src/components/provider-auth/types.ts
  - keep provider-specific command/title behavior and Gemini setup guidance
  - preserve compatibility for both onboarding flow and settings login flow

- Move TaskIndicator into the sidebar domain:
  - add src/components/sidebar/view/subcomponents/TaskIndicator.tsx
  - update SidebarProjectItem to consume local sidebar TaskIndicator

- Update integration points to the new structure:
  - ProtectedRoute now imports onboarding from onboarding feature
  - Settings now imports ProviderLoginModal directly (remove legacy cast wrapper)
  - git panel consumers now import shared GitDiffViewer by explicit name

- Rename git shared diff view to clearer domain naming:
  - replace shared DiffViewer with shared GitDiffViewer
  - update FileChangeItem and CommitHistoryItem imports accordingly

- Remove superseded root-level legacy components:
  - delete src/components/LoginModal.jsx
  - delete src/components/Onboarding.jsx
  - delete src/components/TaskIndicator.jsx
  - delete old src/components/git-panel/view/shared/DiffViewer.tsx

- Result:
  - clearer feature boundaries (auth vs onboarding vs provider-auth vs sidebar)
  - easier navigation and ownership by domain
  - preserved runtime behavior with improved readability and modularity

src/components/chat/view/subcomponents/ProviderSelectionEmptyState.tsx

@@ -2,9 +2,9 @@ import React from 'react';
 import { Check, ChevronDown } from 'lucide-react';
 import { useTranslation } from 'react-i18next';
 import SessionProviderLogo from '../../../llm-logo-provider/SessionProviderLogo';
-import NextTaskBanner from '../../../NextTaskBanner.jsx';
 import { CLAUDE_MODELS, CURSOR_MODELS, CODEX_MODELS, GEMINI_MODELS } from '../../../../../shared/modelConstants';
 import type { ProjectSession, SessionProvider } from '../../../../types/app';
+import { NextTaskBanner } from '../../../task-master';
 
 interface ProviderSelectionEmptyStateProps {
   selectedSession: ProjectSession | null;