docs: reference FolderHome provider pin

[lukisch]

Add a factual FolderHome reference to the KnowledgeDigest English and German READMEs and llms.txt.

The entry points to the exact source revision declared by FolderHome’s component manifest, names the declared documents.index and documents.search effects, and links to the provider-checkout guide. It makes no claim about compatibility with an unpinned or latest revision.

Validation: git diff --check passed; the manifest pin, capability declarations, commit URL, and guide path were checked against the source files and GitHub content. This is documentation-only, so no test suite was run.

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[lukisch]

Reviewed exact head be47b75 against ef7d290. Exactly three documentation lines add the reciprocal FolderHome reference in English/German README and llms.txt. The pinned source revision and declared index/search effects are distinguished from current runtime compatibility; the checkout guide link is correct. All nine checks passed on this head, including Python 3.10-3.13, package artifacts and CodeQL. Ready for the regular merge path subject to unchanged head and repository rules.