Report how the working tree changed, not just which files were overwritten

[achedon12]

After a graft, the report lists the paths the template won a conflict on. That answers which files, but not how much — and a one-line change reads very differently from a rewritten file.

Proposal

Add a line count to each reported path, from git diff --numstat <startSha> HEAD -- <path>:

! The template won 2 conflicted files:
  config/nginx.conf     +12 -3
  src/theme.css         +140 -138

The second line there is the one that should make someone stop and look.

Where to look

applyCommand in src/commands/apply.ts already has result.startSha. The Git class in src/core/git.ts is where a numstat helper belongs.