Add Django 5.2 support and fix duplicate CI runs

[Copilot]

• Update CI workflow triggers to only run on push to main or on PRs (eliminate duplicate runs)
• Add matrix strategy to test with Django 4.2 and Django 5.2
• Update pyproject.toml Django dependency to support Django 5.2
• Regenerate poetry.lock after pyproject.toml changes

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[SupraSummus]

@copilot pyproject.toml changed significantly since poetry.lock was last generated. Run poetry lock to fix the lock file.

[Copilot]

@copilot pyproject.toml changed significantly since poetry.lock was last generated. Run poetry lock to fix the lock file.

Done — ran poetry lock and committed the updated lock file in 87d4c78.