fix: read/write manifests with utf-8 encoding

[InertiaImpact]

This pull request updates several file operations in server/app.py to explicitly specify UTF-8 encoding when opening files. This change improves compatibility and ensures proper handling of non-ASCII characters, especially when reading or writing JSON files.

This also fixes issues where encoding errors cause the settings cogs from rendering/being shown as well as potentially preventing whole apps from being displayed in the list.

File handling improvements:

• Updated all open() calls for reading and writing JSON configuration and manifest files to use encoding='utf-8' in the following functions: load_settings, save_settings, load_installed_plugins, _load_channel_data, and app_library (server/app.py). [1] [2] [3] [4] [5]

[InertiaImpact]

Should add, this fixes an encoding issue where non-standard characters show as garbled text, settings cog to not show, as well as sometimes prevent apps from being listed.

Before:

After: