fix(sounds): fall back when the server has no play-sounds capability

[bakiburakogun]

☑️ Resolves

• Ref Sound setting not saved across restarts talk-desktop#1087 (sound setting not saved across restarts)

Since Talk 24 the sounds store reads the user's "play sounds" setting from the capabilities (config.call.play-sounds). That works against a Talk 24+ server, but servers before Talk 24 don't have that capability at all, so getTalkConfig('local', 'call', 'play-sounds') returns undefined there: sounds are off after every start and the toggle in the settings dialog doesn't stick, which is the talk-desktop issue above again (the 2.2.x desktop client bundles the Talk 24 frontend and still supports NC 32/33 servers), just with the default flipped to silent.

This keeps the capability as the first source and adds fallbacks for older servers:

1. capability (Talk 24+)
2. value remembered in browser storage
3. initial state (play_sounds) that the web page of older servers still provides
4. enabled, as before Talk 24

When the capability is missing, setShouldPlaySounds additionally mirrors the value to browser storage so the next start can pick it up. Guests are unchanged (storage first, then capability, then initial state). Against Talk 24+ nothing changes.

Known limitation on older servers: a change made in another browser/device isn't picked up until the toggle is used locally, since there is no way to read the value back. That's the same trade-off @Antreesy described in the linked issue.

Added a small spec for the store's initial value and the action; the store computes its initial value at import time, so the tests reload the module.

🖼️ Screenshots

n/a

🚧 Tasks

• Code
• Tests

🏁 Checklist

• ⛑️ Tests are included or not possible
• 📘 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk is updated or not required
• 📗 Admin documentation in https://github.com/nextcloud/documentation/tree/master/admin_manual/talk is updated or not required
• 📕 Developer documentation in docs/ is updated or not required
• 🔖 Capability is added or not needed

[nickvergessen]

Hi @bakiburakogun thanks for your frequent involvement. In case you are interested you can send me an email to <my github handle>@nextcloud.com so I can invite you to our Talk Developer chat.
Also the Nextcloud Conference and Contributor Week is happening soon in Berlin, if you are close and want to join us there: https://nextcloud.com/conference-2026/