Fix Citation behavior required by Catalog

[asuworks]

Summary

• fix primary-publication CSV export, including multi-author cell alignment;
• correct SuggestedMerge content-type handling and add migration 0036;
• harden graph, cache, orphan-cleanup, serialization, and URL-validation behavior;
• add behavior-focused regression tests for exports, merges, commands, and URL validation.

This should merge before the Catalog PR so Catalog can pin the resulting upstream Citation commit.

Verification

• Citation system and migration checks pass;
• Citation test suite passes through Catalog CI;
• Catalog integration, export, merge, cache, and URL-validation tests pass.

[Copilot]

Copilot review overview

🟡 Changes recommended

At least one introduced bug in graph filtering date parsing (ISO ...Z handling) will raise at runtime and likely fail the new graphviz tests.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 2

Open (2)

• Reject unsupported many-to-many paths in CSV attributes · New
• Handle Z-suffixed ISO-8601 dates in date filtering · New

What changed in this PR

This PR updates Citation’s export, merge, graph, URL-validation, and notification behavior to match expectations needed by the downstream Catalog integration, and adds targeted regression coverage to lock those behaviors in.

Changes:

• Introduces a transaction-safe publications_changed signal with a notify_publications_changed() helper, and wires it into publication-affecting write paths (serializer saves, merges, URL status updates, admin action, orphan cleanup).
• Reworks primary-publication CSV exporting to keep each publication on a single CSV row (including correct multi-author formatting) and adds coverage for write vs stream parity.
• Hardens graph filtering/aggregation and SuggestedMerge content-type handling (plus migration 0036), with regression tests for the new constraints and behaviors.

File	Description
tests/​test_validate_urls.py	Verifies URL validation continues after request failures and logs failure details.
tests/​test_serializers.py	Adds post-commit notification test for PublicationSerializer.save() and validates merge serializer constraints.
tests/​test_merge.py	Adds end-to-end tests for SuggestedMerge tag merges, signals, and unsupported model errors.
tests/​test_management_commands.py	Ensures orphan cleanup emits publication-change notifications with related IDs.
tests/​test_graphviz_data.py	Adds regression tests for graph filtering/aggregation behavior and immutability of filter criteria.
tests/​test_export_data.py	Confirms CSV export keeps a publication’s data in one row and streaming matches writing.
tests/​test_auditlog.py	Makes audit log contribution tests robust to non-pk=1 publications.
tests/​test_admin.py	Tests curator assignment auditing and post-commit notification behavior.
citation/​signals.py	Adds publications_changed signal and notify_publications_changed() (on-commit, normalized IDs, robust receiver error logging).
citation/​serializers.py	Emits post-commit publication-change notifications on PublicationSerializer.save(); restricts SuggestMerge model_name values.
citation/​ping_urls.py	Fixes pattern count logging (len() vs .count()).
citation/​models.py	Improves URL status logging on request failures, adds post-commit notifications, tightens SuggestedMerge supported models, fixes tag merge relationship update, and adds supported-model error.
citation/​migrations/​0036_alter_suggestedmerge_content_type.py	Migration aligning SuggestedMerge content-type constraints with supported models.
citation/​management/​commands/​validate_urls.py	Fixes misplaced debug log statement indentation.
citation/​management/​commands/​remove_orphans.py	Wraps in a transaction and emits post-commit notifications for removed orphan IDs.
citation/​management/​commands/​cache_data.py	Normalizes log message casing and minor import ordering.
citation/​graphviz/​data.py	Replaces Haystack-based filtering with ORM-based filtering and updates aggregation logic.
citation/​export_data.py	Refactors CSV exporter to support nested FK attributes, stable author aggregation, and consistent streaming output.
citation/​apps.py	Sets AppConfig.path for the app module.
citation/​admin.py	Makes curator assignment atomic/bulk-audited and emits post-commit notifications.

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[alee]

LGTM, thanks Anton! Minor comments on tests but no blockers