feat: extract API services and refactor components to use apiClient

[AdityaK9822]

Description

This PR modernizes the frontend API integration by systematically extracting scattered inline fetch calls from UI components into centralized, domain-specific service classes.

All API interactions are now routed through the apiClient, ensuring consistent communication, centralized error handling, and end-to-end type safety across the frontend application.

Closes #432

What I Did

• Expanded Domain Services: Created and expanded service files in src/lib/api/* (employees.ts, finance.ts, team.ts, kyb.ts, auth.ts, organization.ts) to encompass all endpoints previously hardcoded in UI components.
• Refactored UI Components: Migrated components to import methods strictly from the domain services instead of defining fetch configurations internally. Key components updated include:
  • AccountManagement & AccountForm
  • AddFundsModal
  • RegistrationWizard & business-details
  • CompleteKYB & CreateTimeOffForm
  • Relevant page files in finance, team, invite, and settings
• Added apiClient PATCH support: Introduced a patch HTTP method to the core API client.
• Handled Edge Cases: Successfully abstracted multi-step presigned S3 upload flows (e.g., Logo and KYB documents) into the service layer while maintaining required external PUT requests.

Testing & Verification

• Checked the frontend directory to verify that no internal /api/v1/ inline fetch calls remain.
• Validated that all frontend components conform cleanly to the new service class TypeScript interfaces.
• Ensured error payloads from the API correctly bubble up via the normalized RequestError handling.

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