tlc: compare files (Ctrl-d) — LCS-based diff viewer dialog
New compare.rs module with CompareDialog showing line-by-line diff
of two files (active panel cursor vs other panel cursor). Uses
LCS dynamic programming algorithm for optimal diff.
Color-coded output: context lines (foreground), removed lines
(error/red, bold), added lines (info/green, bold). Supports
scrolling (arrows, PageUp/Down, g/G for Home/End).
Error handling for unreadable files. MAX_LINES=10000 OOM guard.
10 new tests covering diff algorithm edge cases and dialog lifecycle.
986 tests total, 0 failures.
vasilito
6ade75f02b