[codex] Improve remote clone SSH failures

[adamziel]

What it does

Makes forkpress remote clone fail faster and with a useful diagnostic when SSH/rsync cannot reach the remote site.

The CLI now:

• adds a 10-second SSH connect timeout to ForkPress-driven SSH commands
• validates an explicitly supplied --ssh-key path before starting rsync
• captures failing rsync stderr and classifies common failures: timeout, connection refused, permission denied, and bad remote path
• prints a copy-paste ssh ... 'test -f .../wp-load.php' command for verifying the target outside ForkPress
• updates the remote-site docs with the same diagnostic command

Rationale

A timed-out SSH port currently surfaces as raw ssh/rsync output followed by forkpress: rsync exited with exit status: 255. That hides the actual next step: confirm the host's SSH port/firewall/IP allowlist before debugging WordPress import or COW branching.

Implementation

remote_clone_command now runs rsync through Command::output() so ForkPress can shape the error instead of losing context after rsync exits. The remote clone SSH helper adds ConnectTimeout=10, and the error formatter includes the exact remote wp-load.php preflight command with shell-safe quoting.

Testing instructions

Checked locally:

cargo fmt --check
FORKPRESS_RUNTIME_BUNDLE=/dev/null cargo test -p forkpress-cli remote_clone
git diff --check