fix: preserve commit message when canceling reword mode

[YuriNachos]

Summary

• When using r to reword a commit message and pressing ESC, the message is now preserved
• This makes reword mode consistent with normal commit behavior
• Simple one-line change: PreserveMessage: false → PreserveMessage: true

Changes

• Modified reword() method in pkg/gui/controllers/local_commits_controller.go
• Changed PreserveMessage flag from false to true

Motivation

Fixes #5183 - users often need to press ESC to look at changes while editing a commit message, and the message was lost when returning to reword mode

Test manual

1. Select any commit
2. Press r (reword)
3. Change message to "Test message 123"
4. Press ESC
5. Select the same commit again
6. Press r

Expected: Message "Test message 123" is present ✅

Behavior note

• The preserved message is stored in .git/LAZYGIT_PENDING_COMMIT (same file as normal commit)
• If you reword multiple commits, only the last message is preserved
• This is consistent with how normal commit mode works

Checklist

• Code compiles (go build)
• Code formatted with gofumpt
• Commit message follows conventional commits