Update README — WEBLATE_ADD_APPS, Routes, and Celery

[AuraMindNest]

Problem

The README was missing sections on WEBLATE_ADD_APPS, HTTP routes, and the Celery task, leaving operators without guidance on app registration, URL setup, and async execution.

Acceptance Criteria

• Architecture diagram includes endpoint/ and shows AppConfig.ready() → real_patterns.
• WEBLATE_ADD_APPS section explains the env var, compares it to settings_override.py, and warns against using both.
• Routes section lists all three endpoints and explains why explicit real_patterns mutation is required.
• Celery task section covers the request→dispatch→worker flow, task signature, and BoostComponentService steps.

Implementation Notes

• WEBLATE_ADD_APPS and settings_override.py must not both be used — doing so duplicates the app in INSTALLED_APPS and raises ImproperlyConfigured at startup.
• Routes are not auto-discovered from INSTALLED_APPS; BoostEndpointConfig.ready() appends to weblate.urls.real_patterns explicitly.
• Celery task passes user_id (not User) because arguments are JSON-serialized; trail=False prevents unbounded result-backend growth.

References

• README.md