Reset current Settings.json from Windows installer

[Blackspirits]

Summary

The Windows installer reset task still checks/deletes only legacy Settings.xml, while current Subtitle Edit settings are stored in Settings.json. Selecting reset can therefore leave the active settings untouched.

This change:

• detects either current Settings.json or legacy Settings.xml
• deletes Settings.json when the reset task is selected
• retains legacy XML cleanup for compatibility
• changes only the installer reset detection/delete entries

Current-base verification

• the defect is still present on upstream fa6d8623c2adb0c646b6d31a11b221b855339bbe
• Subtitle_Edit_Installer.iss is byte-for-byte identical between the reviewed internal PR Reset current Settings.json from Windows installer #18 base and current upstream
• the reviewed one-file fix was therefore ported exactly onto the current upstream tree
• current diff is one commit, one file, +5/-2 lines
• full solution restore passed
• full solution build passed
• full solution test suite passed on the first run
• retry step was not used
• validation run: #34725476046

Base is current upstream fa6d8623c2adb0c646b6d31a11b221b855339bbe.

This PR supersedes internal draft #18.

AI assistance: ChatGPT was used to independently re-audit the installer reset path on current upstream, verify exact base-file identity, and port the compatibility-preserving fix without unrelated changes.

[Blackspirits]

Independent adversarial re-check on current upstream base: confirmed the installer still detects/deletes only legacy Settings.xml while active settings live in Settings.json. This exact one-file fix updates reset detection and deletion for Settings.json while retaining legacy XML cleanup. Full current-base CI run #34725476046 passed restore/build/full tests on the first run with no retry. HEAD a89cb7d1... is unsigned. No blocker identified. Keep draft; no merge/promotion performed.