GitHub person-mode: author-scoped queries when the topic is a person

last30days switches GitHub from keyword search to author-scoped queries when the topic is a person: PRs merged and merge rate, own repos with stars and README summaries, recent releases. That answers 'what are they shipping' rather than 'who mentioned this name in an issue'.

last30flames already uses the official GitHub API, so this is fully within constraints: detect (or accept via flag, e.g. `--github-user=steipete`) a GitHub login and query commits/PRs/repos/releases scoped to that author within the recency window, rendering them into the numbered context.

Start by reading the existing last30days and last30flames GitHub API entry points to understand how topics, recency windows, and numbered context are handled. Trace the current keyword-search flow, then define the author-scoped behavior for commits, PRs, repositories, and releases, including the optional --github-user flag. Done means a person topic produces author-focused results within the recency window while other topics retain their existing behavior.

Written by the indexing model from the issue text.