feat: implement Data Migration page - Excel upload, history, filters, send to Loan Queue

[Abd1920]

Data Migration Feature Implementation

Overview

A new Data Migration page for data-entry role users to import historical
loan data from Excel files into the IDB system.

New Files

• Client/src/pages/DataMigration.jsx - Full migration UI
• server/src/models/migratedLoan.js - MigratedLoan MongoDB model
• server/src/controllers/migrationController.js - Upload, list, send to queue, delete
• server/src/routes/migrationRoutes.js - API routes

Features

Upload Tab

• Drag & drop or click to browse Excel files (.xlsx, .xls)
• Excel format requirements guide with required/optional fields
• Step-by-step migration process guide
• Download Excel template button
• Import result summary (total, imported, skipped rows)
• Skipped row error details shown after upload

Migration History Tab

• All imported records with migration status badges
• Checkbox selection (individual + select all)
• Send selected records to Loan Queue
• Delete individual records
• Search by name or NIC
• Filter by Region, Sector, Batch
• Clear all filters option
• Pagination

Sent to Queue Tab

• Records already sent to Loan Queue
• View in Loan Queue button per record
• Same filter options

Tab Persistence

• Active tab saved in sessionStorage
• Refreshing browser stays on current tab

Backend

• POST /api/migration/upload - Parse Excel, validate rows, save to DB
• GET /api/migration - List with search, region, sector, batch filters
• GET /api/migration/batches - Grouped batch summary
• POST /api/migration/send-to-queue - Create real Loan records from selected
• DELETE /api/migration/:id - Remove migration record

Packages Installed

• xlsx - Excel file parsing
• uuid - Unique batch ID generation
• multer - File upload handling (memory storage)

Access Control

• Only data-entry role can access /migration route
• Protected at both route level (App.jsx) and sidebar level