[FEATURE] Diff options, especially ignore whitespace (re-opening #7599)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

This is no different from #7599, which was closed prematurely due to a bug in the issue management bot. I'm copying its text here:

When claude code calls Update on a file in default mode (not "plan" or "auto accept edits") diffs are shown with whitespace changes and with unconfigurable context size.

Proposed Solution

• Add global configuration options for "ignore whitespace changes" (-b, --ignore-space-change in GNU diffutils diff and in git diff) and diff context size (-U<n>, --unified=<n>)

Alternative Solutions

• Allow changing these options interactively in the menu when the "Update" diff is shown to user
• Allow user to provide alternate diff command (so I can put in 'diff -uw' or something).

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

I require claude to line up related syntax in my code:

foo    = require 'foo'
bumble = require 'bumble'

When I add foobiebletch = require 'foobiebletch', Claude correctly re-aligns the equals, but the diff doesn't need to show them as changed. This is the same use case that all diff tools have for ignoring whitespace.

Additional Context

_No response_