[stable33] fix(user): prose quality fixes across user manual (MED severity)

[backportbot]

Backport of #14642

Warning, This backport's changes differ from the original and might be incomplete ⚠️

Todo

• Review and resolve any conflicts
• Review and verify the backported changes
• Remove all the empty commits
• Amend HEAD commit to remove the line stating to skip CI

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[skjnldsv]

@copilot base on #14642 original PR, fix the failed rebase

[Copilot]

@copilot base on #14642 original PR, fix the failed rebase

Fixed in e867d6d. The stable33 branch has a different Talk file structure — the files changed in the original PR (attachments.rst, call.rst, call_recording.rst, federation_index.rst) don't exist here. I mapped the changes to the equivalent stable33 files:

• talk_basics.rst: "irrespective of them having a user account" → "regardless of whether they have a Nextcloud account" (was in attachments.rst)
• talk_basics.rst: simplified the circular push-to-talk description (was in call.rst)
• advanced_features.rst: "some time" → "a few seconds" for recording processing (was in call_recording.rst)

The federation_index.rst CloudID definition change has no equivalent content in stable33's federation section, so it was not applied.