feat: build asset notes, document attachments, maintenance records, and transfer workflows

[abdulrcrtw]

Summary of Changes

This pull request implements the backend modules assigned to abdulrcrtw:

• Asset Notes ([BE-89] Asset notes #1142): Built AssetNote entity and endpoints (GET/POST /assets/:id/notes).
• Asset Document Attachments ([BE-90] Asset document attachments #1143): Built AssetDocument entity and endpoints (GET/POST /assets/:id/documents).
• Maintenance Records ([BE-91] Asset maintenance records #1144): Built MaintenanceRecord entity, MaintenanceService, and MaintenanceController supporting scheduled and completed records.
• Asset Transfer Workflows ([BE-92] Asset transfers with an approval workflow #1145): Built AssetTransfer entity, TransfersService, and TransfersController supporting approval (POST /transfers/:id/approve) and rejection (POST /transfers/:id/reject).

Closes #1145
Closes #1144
Closes #1143
Closes #1142

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[yusuftomilola]

Reviewed the diff — matches its description. Adds asset notes and document-attachment endpoints (notes-docs.controller.ts), a MaintenanceModule (scheduled/completed maintenance records), and a TransfersModule with approve/reject endpoints for asset transfer workflows. All new, distinct file paths — no collisions with previously merged assets/ files.

Same recurring app.module.ts additive-registration conflict as the last several PRs (new imports/module registrations landing at the same insertion point as prior merges); combined both since they're independent modules with no functional overlap. Resolved locally and pushed to main. Approving.