Related to #595
This change adds support for custom SSH ports when collecting temperature
data from Proxmox nodes, resolving issues for users who run SSH on non-standard
ports.
**Why SSH is still needed:**
Temperature monitoring requires reading /sys/class/hwmon sensors on Proxmox
nodes, which is not exposed via the Proxmox API. Even when using API tokens
for authentication, Pulse needs SSH access to collect temperature data.
**Changes:**
- Add `sshPort` configuration to SystemSettings (system.json)
- Add `SSHPort` field to Config with environment variable support (SSH_PORT)
- Add per-node SSH port override capability for PVE, PBS, and PMG instances
- Update TemperatureCollector to accept and use custom SSH port
- Update SSH known_hosts manager to support non-standard ports
- Add NewTemperatureCollectorWithPort() constructor with port parameter
- Maintain backward compatibility with NewTemperatureCollector() (uses port 22)
- Update frontend TypeScript types for SSH port configuration
**Configuration methods:**
1. Environment variable: SSH_PORT=2222
2. system.json: {"sshPort": 2222}
3. Per-node override in nodes.enc (future UI support)
**Default behavior:**
- Defaults to port 22 if not configured
- Maintains full backward compatibility
- No changes required for existing deployments
The implementation includes proper ssh-keyscan port handling and known_hosts
management for non-standard ports using [host]:port notation per SSH standards.
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