feat(init): interactive remote pre-staging via ssh-copy-id

orca init now interactively prompts for remote host addresses and runs
ssh-copy-id automatically (password prompt passes through to the
operator). This makes orca init the single entry point — no manual
pre-staging of SSH keys required.

- Interactive: enter host addresses (one per line, empty line to finish)
- ssh-copy-id deploys the orca public key to each host
- Skipped in --json mode (non-interactive)
- Idempotent: re-running init can stage additional hosts

Also fixed: install.sh defaults to /usr/local/bin (on PATH for all users).
Non-root without sudo falls back to ~/.local/bin + auto-adds to .bashrc.

docs/uat.md

@@ -44,15 +44,11 @@ orca init
 - Traefik data-plane ingress (binary + systemd unit + config)
 - Localhost node registered
 
-**Pre-staging remote nodes**: `orca init` prints the orca public key path.
-Deploy it to each remote host before joining:
-```sh
-ssh-copy-id -i $ORCA_HOME/orca_ssh_key.pub root@pve01
-ssh-copy-id -i $ORCA_HOME/orca_ssh_key.pub root@worker01
-```
-
-The TOFU host-key capture is automatic — no manual fingerprint pinning needed.
-The first SSH connection captures and stores the remote host key.
+**Pre-staging remote nodes**: `orca init` interactively prompts for remote
+host addresses and runs `ssh-copy-id` automatically (password prompt passes
+through). Enter each host (pve01, worker01) when prompted, or press Enter to
+skip. The orca public key is deployed to each host; TOFU host-key capture is
+automatic on the first `orca node join` — no manual fingerprint pinning needed.
 
 ### Step 2: Onboard the Proxmox host