Implement navigation progress indicator and account invitation feature

[seriwb]

This pull request introduces several enhancements and refactors to the admin application, focusing on improved navigation handling, user experience, and account management features. The most notable changes are the migration to a custom navigation hook for routing, the addition of an account invitation email feature, and documentation updates for clearer setup and structure. Below are the top changes grouped by theme:

Navigation and Routing Improvements:

• Replaced direct usage of Next.js's useRouter with a custom useNavigationRouter hook across multiple components (edit-account.tsx, account-list.tsx, account-search.tsx, create-account.tsx), standardizing navigation logic and simplifying code. (apps/admin/src/app/(app)/system/accounts/[id]/edit/_parts/edit-account.tsxL4, apps/admin/src/app/(app)/system/accounts/[id]/edit/_parts/edit-account.tsxR23, apps/admin/src/app/(app)/system/accounts/[id]/edit/_parts/edit-account.tsxL33-R33, apps/admin/src/app/(app)/system/accounts/[id]/edit/_parts/edit-account.tsxL57-R57, apps/admin/src/app/(app)/system/accounts/[id]/edit/_parts/edit-account.tsxL78-R78, apps/admin/src/app/(app)/system/accounts/[id]/edit/_parts/edit-account.tsxL202-R202, [1] [2] [3] [4] [5] [6] [7] [8]
• Introduced NavigationProgressProvider in app-layout.tsx to enable navigation progress tracking, and added a visual indicator component (link-indicator.tsx) for page transitions. [1] [2] [3] [4] [5]

Account Creation and Invitation Email Feature:

• Added a sendInvite boolean field to account creation forms and schema, allowing admins to optionally send an invitation email to new accounts. [1] [2] [3] [4]
• Updated the accounts API route to send an invitation email using a new template (InviteEmail) and mail utility when sendInvite is enabled. Errors in sending mail no longer block account creation. [1] [2] [3]

UI Consistency and Refactoring:

• Replaced usage of Next.js's Link component with a custom Link component throughout navigation and sidebar files for consistent styling and behavior. [1] [2]

Documentation and Environment Updates:

• Revised README.md and apps/admin/README.md to clarify project structure, setup steps, and local development tips, including infrastructure details and mail confirmation instructions. [1] [2]
• Updated .env.template to include SES endpoint and mail sender settings for local development.