Support --summary on show, log and diff #17

Summary

--summary isn't supported on git show, git log or git diff. Each one fails with exit 1:

Unknown option "--summary".
Not all git options are supported. Run 'git <command> --help' for available options.

Agents use git show --stat --summary and git log --summary to see what a commit created, deleted or re-moded. Right now the whole command fails, so they get none of the output, not even the commit.

Repro (just-git 1.9.1 + just-bash 3.6.0)

mkdir s && cd s && git init -q
echo a > a && printf 'x\n' > run.sh && chmod 755 run.sh && git add -A && git commit -q -m one
git rm -q a && echo b > b && chmod 644 run.sh && git add -A && git commit -q -m two
git show --stat --summary --format=%s HEAD; echo rc=$?
git log --summary --format=%s -1; echo rc=$?
git diff --summary HEAD~1 HEAD; echo rc=$?

just-git 1.9.1: the error above three times, rc=1 each time.

git 2.34.1:

two

 a      | 1 -
 b      | 1 +
 run.sh | 0
 3 files changed, 1 insertion(+), 1 deletion(-)
 delete mode 100644 a
 create mode 100644 b
 mode change 100755 => 100644 run.sh
rc=0
two

 delete mode 100644 a
 create mode 100644 b
 mode change 100755 => 100644 run.sh
rc=0
 delete mode 100644 a
 create mode 100644 b
 mode change 100755 => 100644 run.sh
rc=0

Most of it exists already

src/lib/commit-summary.ts already builds these lines for the summary printed after git commit (create mode, delete mode, rename ... (N%)). --summary could reuse that list, printed after the stat block (or alone, when no other diff format is selected).

One difference to fix while there: for a permission-only change, commit-summary.ts L141–L144 pushes a delete mode and a create mode line. Git prints mode change 100755 => 100644 <path> when both sides are regular files, and keeps delete + create only for type changes such as file to symlink. So today git commit after a chmod shows

 create mode 100644 run.sh
 delete mode 100755 run.sh

where git shows mode change 100755 => 100644 run.sh. (Cited at b509001, 1.9.1.)

Suggested scope

--summary on show, log and diff, combinable with --stat, --shortstat, --numstat and --name-only/--name-status the way git allows. Lines: create mode, delete mode, mode change <old> => <new>, and rename <path> (<similarity>%) / copy.

Low priority. git log -1 --name-status and git diff --name-status show added and deleted files. A mode change appears only as M, and git ls-files -s shows the current mode but not the old one.