Add "et al." to invalid citation examples in prompt

[jamesbraza]

Summary

CITATION_KEY_CONSTRAINTS lists invalid citation formats to steer LLMs toward using pqac-* citation keys. However, all the invalid examples only show wrong ways to format pqac-* keys themselves -- there is no example prohibiting academic-style author citations.

In practice, on long answers the answer LLM occasionally slips in citations like Deschamps et al. (2004) alongside otherwise correct pqac-* keys. The existing prompt instructions ("only use the valid keys") are not always sufficient to prevent this.

This PR adds - Author et al. (2023) as an invalid citation example so the constraint explicitly covers this failure mode.

Made with Cursor

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Note

Low Risk
Low risk: this only tweaks prompt text to further constrain LLM citation formatting, with no code-path, security, or data-handling changes.

Overview
Tightens CITATION_KEY_CONSTRAINTS in prompts.py by adding Author et al. (2023) as an explicit invalid citation example to reduce the model mixing academic-style citations with pqac-* keys.

Also fixes a missing trailing newline in the existing invalid example - (pages pqac-d79ef6fa) to keep formatting consistent.

^{Written by Cursor Bugbot for commit 6abce43. Configure here.}

[Copilot]

Pull request overview

Updates the CITATION_KEY_CONSTRAINTS prompt in paperqa to more explicitly discourage non-pqac-* academic-style author/year citations (e.g., “et al.”) that sometimes appear in long-form model outputs.

Changes:

• Adds - Author et al. (2023) to the “Invalid citation examples” list.
• Ensures the preceding invalid example line ends with a newline so the new bullet renders separately.

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