fix(QDialog): preserve sticky elements in Firefox (#18183)

[devel-maverick]

What kind of change does this PR introduce?

• [x] Bugfix
• [ ] Feature
• [ ] Documentation
• [ ] Code style update
• [ ] Refactor
• [ ] Build-related changes
• [ ] Other, please describe:

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

The PR fulfills these requirements:

• [x] It's submitted to the dev branch (or v[X] branch)
• [x] When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #18183, #18185)
• [ ] It's been tested on a Cordova (iOS, Android) app
• [ ] It's been tested on an Electron app
• [x] Any necessary documentation has been added or updated in the docs or explained in the PR's description.

If adding a new feature, the PR's description includes:

• [ ] A convincing reason for adding this feature (to avoid wasting your time, it's best to start a new feature discussion first and wait for approval before working on it)

Other information:

This PR fixes two QDialog issues:

1. #18183 – Sticky elements disappearing in Firefox when opening QDialog.

   • Solution: Removed position: fixed and left/top adjustments; now using overflow: hidden and padding-right to preserve layout and scrollbars.

2. #18185 – Scroll position not restored if URL changed.

   • Solution: Scroll restoration now considers only the pathname. If pathname unchanged, scroll is restored even if query/hash changed.

Tested on Firefox, Chrome, and Safari. iOS-specific behavior retained.