Adds --doc (repeatable, file or directory) so the researcher can draw on
user-supplied documents alongside the web: documents.rs resolves paths
into embeddable text, retrieval.rs embeds them with a dedicated
embedding model (nomic-embed-text, separate from the chat models used
elsewhere) into an in-memory vector index and retrieves the excerpts
most relevant to the topic once up front, and researcher.rs folds those
excerpts into the researcher's task under the same footnote-citation
scheme already used for web sources. The embedding and retrieval phases
show progress the same way every other phase does — a spinner while
embedding, a summary line once excerpts are retrieved, tracing spans
for -l mode.
Verified against a live Ollama nomic-embed-text pull and a real
research round: a planted fact sheet was correctly ranked as the most
relevant of several embedded documents and appeared in the researcher's
task before its first turn.
