Update all UI texts to consistently use sentence case instead of title case

[tjementum]

Summary & motivation

Update all UI text to consistently use Sentence case instead of Title Case for a more modern and consistent interface. This change affects:

• Buttons (e.g. "Delete account" instead of "Delete Account")
• Menu items (e.g. "View profile" instead of "View Profile")
• Headings (e.g. "Account settings" instead of "Account Settings")
• Form labels (e.g. "User role" instead of "User Role")
• Placeholders (e.g. "Software engineer" instead of "Software Engineer")

The change also updates the translation AI rules to explicitly specify that buttons, menus, and headings must use sentence case.

Downstream projects

For maintainers of downstream projects, you should:

1. Update your UI text

Look in your .po files and identify all places you use Title Case, then find the places in your code where the translation is coming from and change these to Sentence case.

2. Update translations

After updating the text, run pp translate from your project root directory to update all translation files.

Checklist

• I have added tests, or done manual regression tests
• I have updated the documentation, if necessary

[linear]

PP-362 Use sentence case in all UI for a modern consistent interface

[sonarqubecloud]

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