Address PR review comments: localize error messages, fix deprecated method, use spacing tokens

[Copilot]

Breaking change

Proposed change

Addresses PR review comments from #28245:

• Localize hardcoded error messages: Replace hardcoded strings with hass.localize() calls in supervisor-app-audio.ts and supervisor-app-info.ts
• Fix deprecated method: Replace .substr() with .substring() in supervisor-app.ts
• Use spacing tokens: Replace hardcoded 8px with var(--ha-space-2) in supervisor-apps-style.ts
• Add translation keys: Add failed_to_load_hardware, failed_to_save, and validate_config to en.json

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example configuration

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion: Add apps panel as built-in panel #28245
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

---

Note

Localizes error messages in app audio/info views, replaces deprecated substr with substring, standardizes spacing via tokens, and adds required translation keys.

• UI/i18n:
  • Localize error messages in config/supervisor-app-audio.ts and info/supervisor-app-info.ts using hass.localize.
  • Add translation keys in translations/en.json for audio.failed_to_load_hardware, audio.failed_to_save, and action_error.validate_config.
• Utilities:
  • Replace deprecated substr with substring in util/supervisor-app.ts (extractChangelog).
• Styles:
  • Use spacing token var(--ha-space-2) instead of hardcoded 8px in resources/supervisor-apps-style.ts.

^{Written by Cursor Bugbot for commit 1430e32. This will update automatically on new commits. Configure here.}