git: delta options, difftastic aliases, delta as lazygit pager

difft is a cargo install on sctfw004 (not in Ubuntu repos), so
pkg-snapshot does not track it there.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

common/git/config

@@ -12,3 +12,12 @@
     pager = delta
 [interactive]
     diffFilter = delta --color-only
+[delta]
+    navigate = true      # n/N jump between files
+    line-numbers = true
+[merge]
+    conflictStyle = zdiff3
+# Structural diffs via difftastic, on demand; delta stays the default pager.
+[alias]
+    dft = -c diff.external=difft diff
+    dlog = -c diff.external=difft log -p --ext-diff

common/lazygit/config.yml

@@ -0,0 +1,4 @@
+git:
+  paging:
+    colorArg: always
+    pager: delta --dark --paging=never