feat(settings): implement system-wide settings module with CRUD APIs

[mdauwal]

Overview

This PR introduces a Settings Module to manage system-wide configurations at the company level.
It includes entity definitions, DTOs, service, controller, and module setup with CRUD support.

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🔨 Changes Introduced

• Entity: Setting with fields:
  • defaultCurrency (default: USD)
  • timezone (default: UTC)
  • depreciationMethod (default: straight_line)
• DTOs: CreateSettingDto & UpdateSettingDto with validation rules
• Service: CRUD methods (create, findAll, findOne, update, remove)
• Controller: REST endpoints for managing settings
• Module: Registered SettingsModule with TypeOrmModule integration

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📡 Endpoints

Method	Endpoint	Description
POST	/settings	Create a new setting
GET	/settings	Retrieve all settings
GET	/settings/:id	Retrieve a setting by id
PATCH	/settings/:id	Update a setting
DELETE	/settings/:id	Remove a setting

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✅ Notes

• Validated with class-validator decorators
• Supports extension for additional system-wide configuration fields
• Exported SettingsService for reuse in other modules if needed

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🎯 Next Steps

• Add authentication/authorization (e.g., admin-only access)
• Seed default system setting on fresh installation

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Closing

closes #335

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