Add citation-needed skill

citation-needed/SKILL.md

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+---
+name: citation-needed
+description: Provide live, verifiable links when a factual claim is challenged with "citation needed", or when asserting a fact likely to be challenged. Formats citations as blockquote markup with the page title as the link and a date. Not for code references or repo-local docs.
+---
+
+# Citation Needed
+
+As established by Wikipedia, [citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed) is a convention for requesting a citation to back a claim. When a claim is challenged this way, or when asserting a fact a skeptical reader might challenge, back it with real sources — not assertions dressed up as citations.
+
+## What counts as evidence
+
+- Live, working links the reader can open and verify. If you only produced
+  links from a search, say the search was the basis and where you looked.
+- Be honest about strength. If every source is a consumer how-to and there is
+  no rigorous study, say so. Do not let the absence of a hard statistic be
+  papered over by confident prose.
+- Retract the parts you cannot support. A partial retraction with the
+  well-supported remainder standing is a stronger answer than a blanket
+  "I was wrong."
+
+## Citation format
+
+Use blockquote markup, a dash, and the page title as the link. Never paste
+raw in-your-face URLs.
+
+- Prefer the page title as the link text.
+- Give the date the source made the claim.
+- Month + year is the default. Within the last month or two, add the day.
+- Within the last day or so, add the time as well.
+- If the date is unknown, say "date unknown" rather than inventing one.
+
+```
+> "quote of the claim being cited."
+> — [Source Page Title](https://example.com/path), Site Name, Sep 23, 2026
+```
+
+## Search hygiene
+
+If you are the one asserting a fact, do a quick search before stating it as
+certain. If the searches you ran turned up only supporting sources and no
+contrary evidence, that is fair to state — but only within the limits of what
+you actually searched.
+
+## Scope
+
+This governs factual claims and their citations. It does not govern code
+references (`file:line`) or pointing at repo-local authoritative docs, which
+are handled by the normal working conventions.