feat: create back button submission form modal

[ShizuokaTerrier]

Resolves #700

🔧 What changed

A modal was added that only triggers on use of the back button in the browser.

🧪 Testing instructions

No tests were added.

📸 Screenshots

• Before

It didn't exist before.

• After

https://github.com/user-attachments/assets/62b0dcf1-436b-45ec-a8b5-77c3f0afb8f5

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[ShizuokaTerrier]

Got a lot of support from @ProgressChris88 in the initial stage and an enormous amount of help in solving the mystery of the maddeningly inconsistent modal from @NabbeunNabi. Big thanks guys.

[theyokohamalife]

Great work getting the modal working! First thought that comes to mind is that we probably only want it to appear if there are actual unsaved changes. I noticed in the demo video that the modal opened if a user navigated to the edit page and hit the back button without making any changes.

[theyokohamalife]

Nit: As a good practice, commit message titles should be limited to about 50 characters. Anything longer than that could be added to the message body. You may want to think about how you could write this message more concisely:

[theyokohamalife]

@all-contributors please add @ShizuokaTerrier for coding

[allcontributors[bot]]

@theyokohamalife

@ShizuokaTerrier already contributed before to code