feat: enable external integrations through API

[its-gabo]

Overview

This PR introduces integration API key support end-to-end and extends the integration API with a tenant listing endpoint.

Implemented scope includes:

• Added backend integration module with dedicated API endpoints, service/repository layer, tenant-aware guard, schemas, and DB migrations for integration API keys.
• Added admin-facing API and frontend settings UI for viewing and rotating integration API keys.
• Updated generated API client, locale strings, Swagger schemas, and supporting bootstrap/module wiring.
• Added endpoint to list tenants and made X-Tenant-Id optional for that specific integration route.
• Added/updated e2e coverage for integration controller behavior.

Business Value

• Enables secure machine-to-machine integrations through dedicated API keys.
• Gives admins a straightforward way to manage integration credentials from the product UI.
• Supports multi-tenant integration scenarios by exposing tenant listing where needed.
• Improves maintainability and adoption with documented API contracts and typed client updates.

Screenshots / Video

Screen.Recording.2026-02-16.at.11.13.22.mov