fix: pre-create ~/.ssh/known_hosts if it doesn't exist

[rfay]

The CLI was failing when users didn't have a ~/.ssh/known_hosts file. Now creates both the .ssh directory (0700) and known_hosts file (0600) with proper permissions if they don't exist. It's not really valid to assume that it already exists (and it doesn't in a test environment like DDEV's automated tests)

It used to fail on lagoon ssh for example:

$ lagoon ssh -p amazeeio-ddev -e pull
Error: couldn't refresh token: couldn't get ~/.ssh/known_hosts: couldn't get ~/.ssh/known_hosts: open /home/rfay/.ssh/known_hosts: no such file or directory
Usage:
  lagoon ssh [flags]

This also fixes the odd output

[INFO]  2026/01/27 22:02:31 Running the following prerequisite command /usr/local/bin/lagoon-sync config || true
[WARN]  2026/01/27 22:02:31 ssh: no key found &{0xc000078120}
[WARN]  2026/01/27 22:02:40 'lagoon-sync' is not available on pull

I think lagoon-sync config just failed because known_hosts wasn't there, leading the logic to conclude that there was no lagoon-sync.

This was discovered exploring the problems in

• panic in utils.RemoteShellout lagoon-sync#135

• Affected Issues have been mentioned in the Closing issues section
• Documentation has been written/updated
• PR title is ready for inclusion in changelog