Django 6.0 requires django.contrib.postgres to be explicitly added to
INSTALLED_APPS when using PostgreSQL-specific features like SearchVectorField
and GinIndex.

This fixes the Heroku deployment error:
wagtailsearch.IndexEntry: (postgres.E005) 'django.contrib.postgres' must be
in INSTALLED_APPS in order to use SearchVectorField and GinIndex.

Fixes deployment issue with Django 6.0 upgrade from PR #179.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

* 🚀 feat: upgrade to Django 6.0

Upgrade Django from 5.2.9 to 6.0 by updating requirements files.

- Update requirements/main.txt: Django 5.2.9 → 6.0
- Update requirements/dev.txt: Django 5.2.9 → 6.0
- All 33 tests pass successfully
- Wagtail 7.2.1 supports Django 6.0

Django 6.0 was released on December 3, 2025:
https://docs.djangoproject.com/en/6.0/releases/6.0/

Wagtail 7.2.x supports Django 6.0:
wagtail/wagtail#13622

Closes #173

* fix: add django.contrib.postgres to INSTALLED_APPS for Django 6.0

Django 6.0 requires django.contrib.postgres to be explicitly added to
INSTALLED_APPS when using PostgreSQL-specific features like SearchVectorField
and GinIndex.

This fixes the Heroku deployment error:
wagtailsearch.IndexEntry: (postgres.E005) 'django.contrib.postgres' must be
in INSTALLED_APPS in order to use SearchVectorField and GinIndex.

Fixes deployment issue with Django 6.0 upgrade from PR #179.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

* fix: configure PostgreSQL for CI tests and move psycopg to main dependencies

Changes:
- Add PostgreSQL 17 service to GitHub Actions workflow
- Configure tests to use PostgreSQL in CI (via DATABASE_URL) while keeping SQLite for local development
- Move psycopg[binary] from production.in to main.in since django.contrib.postgres is now in base INSTALLED_APPS
- Update workflow to install production.txt dependencies
- Recompile all requirements files

This fixes the test failure where django.contrib.postgres required psycopg to be installed
but it was only available in production dependencies, not in the CI test environment.

The conditional database configuration in tests.py allows:
- CI: Uses PostgreSQL (matching production environment)
- Local dev: Uses SQLite (simpler setup without PostgreSQL requirement)

Fixes the Django 6.0 compatibility issue from the previous commit.

---------

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>