Description
When a file has git conflict markers (<<<<<<< HEAD / ======= / >>>>>>> branch, plus ||||||| base for diff3), highlight the marker lines in bold and tint the two version blocks in slightly different background colors. Implemented as a post-pass over scanned spans in buildVisual so it applies to both prose (.md/.txt) and code files. Adds ConflictMarker/ConflictOurs/ConflictTheirs theme colors.
Acceptance Criteria
- #1 Conflict marker lines (<<<<<<<, |||||||, =======, >>>>>>>) render bold in a distinct color
- #2 The 'ours' and 'theirs' blocks between markers get slightly different background tints
- #3 Markers only detected inside a conflict block (no false hits on setext ===== or ==highlight==)
- #4 Works in both prose and code files; markup-visible invariant preserved