fix(ui): send the Show Changes prompt when launching a job

[MateusRoscoe]

SUMMARY

Assisted-by: Claude Opus 5.5. Drafted with AI assistance; the commit carries the same trailer.

With Prompt on launch enabled for Show Changes, turning the toggle on in the launch wizard had no effect: the job ran with diff_mode: false and without --diff. There were two causes, and this fixes both:

• handleSubmit in LaunchPrompt.tsx builds the launch request field by field and never added diff_mode. It now posts diff_mode next to verbosity, in the same way as the other prompted fields. LaunchPromptValues gains the diff_mode?: boolean field.
• ShowChangesToggle in OtherPromptsStep.tsx passed the form setter straight to PatternFly's Switch (onChange={helpers.setValue}). Switch calls onChange(event, checked), so the field held the change event. An object is truthy, so the switch stayed on once clicked and could not be turned off. It now stores checked, and its label shows On or Off, as the Show Changes switch on the job template form already does.

The API side needs no change. It already applies a prompted diff_mode when it is posted.

Fixes #1127

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• UI

ASCENDER VERSION

25.6.2-267-g205e8fd5 (main, the base of this branch)

ADDITIONAL INFORMATION

New tests:

• OtherPromptsStep.test.tsx: should turn show changes on and off again clicks the switch on and then off, and checks its state after each click.
• LaunchPrompt.test.tsx: should launch with show changes when it is turned on and should launch without show changes when it is left off go through the wizard to Launch, and check that onLaunch receives diff_mode: true and diff_mode: false respectively.

# with this change
$ TZ=UTC vitest run src/components/LaunchPrompt
 Test Files  10 passed (10)
      Tests  58 passed (58)

$ TZ=UTC vitest run
 Test Files  555 passed (555)
      Tests  3126 passed (3126)

# main f9cf2733 with only the new tests
$ TZ=UTC vitest run src/components/LaunchPrompt
     × should turn show changes on and off again
     × should launch with show changes when it is turned on
     × should launch without show changes when it is left off
      Tests  3 failed | 55 passed (58)

# eslint, prettier --check and check-strings pass on the changed files

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