Implements ExtractImages() which scans filter stdout line-by-line,
extracts valid OSC 9 image markers into ImageRef structs, and replaces
marker lines with null-delimited placeholders (\x00IMG:N\x00). Invalid
markers (missing path) pass through unchanged. Also clarifies the Index
field comment in ImageRef to indicate it is set by ExtractImages, not
ParseImageOSC.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Mortdecai