feat: Add loading states and improve form handling

This commit introduces several enhancements to form components and user experience across the application.

- **Sign-in Form:**
  - Implemented a loading state using `useIsMutating` from TanStack Query.
  - The username and password fields are now disabled during the login process to prevent concurrent submissions.
  - The "Sign in" button displays a spinner while the mutation is pending, providing clear visual feedback.

- **Assign to Company Modal:**
  - Refactored the modal to use `react-hook-form` for more robust state management and validation.
  - The form submission button is now disabled while the assignment request is in progress.

- **Tag Input Component:**
  - Added a new `shouldAddWithSpace` prop to allow creating tags by pressing the space bar, increasing the component's flexibility.

- **Header:**
  - Corrected the image path for the mobile header logo to display the correct icon.

src/constants/regex.ts

@@ -1 +1,2 @@
 export const PHONE_REGEX = /^[+\d]+$/;
+export const USERNAME_REGEX = /^[a-zA-Z0-9](?:[a-zA-Z0-9._]*[a-zA-Z0-9])?$/;