Function search_documents 

pub async fn search_documents(
    config: &Config,
    query: &str,
    mode: &str,
    source_filter: Option<&str>,
    since: Option<&str>,
    limit: Option<i64>,
    explain: bool,
) -> Result<Vec<SearchResultItem>>

Core search function returning structured results.

This is the shared implementation used by both ctx search (CLI) and POST /tools/search (HTTP server). Delegates to context_harness_core::search::search via SqliteStore.