T19 round 1 fixes

- merges keep each line's ending and the last newline; resolve keeps every other byte
- the split view numbers each side from its own file
- hunk headers come from similar's UnifiedHunkHeader: an empty side starts before its range
- the commit subject counter sits in the input's suffix
- clipped code rows in diffs, merges, blame and review set their line height
- gallery: scripted split view and a long subject

TASKS.md

@@ -242,4 +242,5 @@ Per-component lines live in `tasks/`. Tags there:
 | T18 | 1 | FAIL | a missing folder ran in the app's own; combining marks dropped; Tab skipped the terminal; its wheel scrolled the page too; clear kept find matches; New bash reused the old shell; the dark script typed into the replay |
 | T18 | 2 | FAIL | a folder it could not enter still started the shell elsewhere; links read cluster cells as spaces |
 | T18 | 3 | PASS | |
-| T19 | 1 | — | pending review |
+| T19 | 1 | FAIL | a merge rewrote line endings and added a last newline; the split view numbered its right side from the old file; an empty side started its hunk a line late; the subject counter covered long subjects; clipped code rows had no line height |
+| T19 | 2 | — | pending review |