add relevance feedback skill

[mrscoopers]

What this PR does

Adds qdrant-relevance-feedback as a new leaf sub-skill under search-strategies/relevance-feedback/, at the same level as hybrid-search/. Updates the parent search-strategies/SKILL.md to replace the inline RF content with a reference link and improve the section header and "Use when:" line.

Type

• new skill
• skill improvement

Checklist

• python3 scripts/validate_skills.py passes — 2 warnings: line count (116, intentional — RF requires prerequisite calibration context) and em-dash (pre-existing style)
• skill answers "when?" or "why?", not "how?" — intentionally more procedural: RF requires one-time calibration before use, so the skill covers the setup steps needed to make it work
• skill navigates to docs, does not duplicate or replace them
• description has Use when with 5+ trigger phrases
• leaf skills omit allowed-tools
• ends with ## What NOT to Do section
• no code blocks except minimal snippets when absolutely required
• all doc links go to search.qdrant.tech/md/documentation/ — two exceptions: api.qdrant.tech/api-reference/search/query-points (RF API reference) and pypi.org/project/qdrant-relevance-feedback/ (calibration library), both intentional

Test prompt

I have a context engineering workshop where I create a collection and populate it.
Currently, it uses a tool based on the retrieve_papers_based_on_query in search_engine_query.py,
which uses hybrid search + reranker, and as a dense search arm, it uses text-embedding-3-small, cut to 1024 dims.

I'd love to use text-embedding-3-large as the dense retriever instead for better quality,
but it's too expensive. Is there any cheaper alternative? Use Qdrant skills, recommend something to me.

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[mrscoopers]

Link checker fails because skill is not merged in, and I reference its URL fully from a parent skill doc, as in my experience, agents have troubles navigating downwards, seeing only relative path & having to figure out absolute URL themselves

So I can fix the link checker thing, but I'd like to avoid it, to be honest:)