Onboarding detects existing internal knowledge bases

The onboarding guide now checks, as part of the initial Orient phase, whether the team already has a structured internal knowledge base — a wiki (Notion, Confluence, Coda, Tettra, GitBook, SharePoint), a shared doc repository, or an existing memsprout Space. When one is found, the guide names it, shifts to an import-first strategy (treating the KB as the primary source rather than starting from scratch), and abbreviates the interview to fill only the gaps the KB doesn't cover. If the existing KB is a memsprout Space, the guide searches it first and raises the dedup threshold to avoid near-duplicate captures.