Backend: GET /git/file reads a file at a branch tip (read_file_at_branch)
and slices it to a line window — explicit start/end, a line+context center,
or the whole file capped at 2000 lines. _compute_file_range is the pure
helper (unit-tested).
Frontend: useGitFile hook + CodeSnippet (styled <pre>, line numbers, active-
line highlight — matches git-diff-viewer, no shiki). Wired into FindingCard
so each file:line finding shows the surrounding source. Fail-open: a missing
file renders a muted hint, never breaks the card.
Co-authored-by: Renn F <rennf93@users.noreply.github.com>
