Fix duplicate references + runaway citation tooltips in RAG answers

[lfnothias]

Summary

Fixes two compounding bugs that made small models (e.g. gpt-4o-mini) emit a duplicate, partly-fabricated references block with a degenerate author tooltip — a citation title attribute that looped "H. " ~749 times (2,247 chars).

Prompt (get_system_prompt)

• The citation title attribute previously had to hold the full author list (<All authors>. <Year>. <Title>. <Journal>.) — which small models loop on. Shortened to Title. Year. Journal. (no author list; the grounded reference list keeps the authors). This removes the loop trigger and fixes the live stream (the model never generates it).
• Added an explicit instruction not to write a "References"/"Bibliography"/"Sources" section — the backend already appends the authoritative, grounded list, so the model's self-made one was a duplicate (and a source of fabricated entries).

Defensive sanitizer (collapse_runaway_repeats)

• Collapses any short unit repeated 8+ times in a row, applied to the assistant answer before it is persisted — belt-and-suspenders for the rare case a model loops anyway.

Verification

• Re-ran the triggering condition on a real multi-author paper (nothias-hdr): one ## References section, no runaway repetition, tooltip = "Feature-based Molecular Networking in the GNPS Analysis Environment. 2019." (74 chars vs the old 2,247).
• Sanitizer unit-checked on the real degenerate answer: 6219 → 3979 chars in ~2 ms; normal prose, numbered lists, and table separators untouched.
• 138 passed across prompt/citation/reference/route unit tests locally.

Note: the test CI job fails on a pre-existing test_web_app_routes.py issue already present on main (the CI "safe subset" sandbox registers no API routers); it passes locally (30/30) and is unrelated to this change.

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