[Git] Stop inlining binary literals in the per-commit diff

[KCaverly]

DiffCommit/NumstatCommit passed --binary, which the branch-wide
DiffAgainstBase never did. --binary is for producing appliable patches: it
makes git inline a base85 "GIT binary patch" literal for every changed
binary file. A 3KB blob expands to 123 lines; a few hundred KB is enough to
exhaust the viewer's 20k-line cap and leave the preview pane showing
nothing but base85.

It also mis-colours: git's base85 alphabet includes + and -, so the diff
body styler paints scattered literal lines as additions and deletions.

Dropping the flag yields the usual one-line "Binary files a/x and b/x
differ", matching DiffAgainstBase. The numstat path is unaffected — it
already reported binary files as Binary with zero counts, so the file index
still renders them as "binary".

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com

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Stack (bottom → top):

1. [Git] Stop inlining binary literals in the per-commit diff #38 ← this PR
2. [UI] Re-prime the stack preview when the status behind it changes #39
3. [Git] Stop returning quoted, octal-escaped untracked paths #40
4. [Git] Add DiffUntracked to render untracked file contents #41
5. [UI] Show uncommitted work as a row in the stack #42
6. [UI] Name one way out of the stack preview #43
7. [UI] Give d the preview and esc the way out #44
8. [UI] Drop the branch-diff jump from the stack screen #45
9. [UI] Stop the stack preview overrunning a narrow terminal #46
10. [Git] Pin the diff flags the body parser depends on #47
11. [UI] Teach both diff viewers the same file-jump key #48
12. [Diff] Thread the [diff] config through the viewer and zoom with z #49
13. [Git] Carry diff args and excludes through every diff call #50
14. [Diff] Add the external diff pager package #51
15. [Config] Accept a [diff] section with an optional pager #52
16. [Docs] Document the diff viewer settings #53