Add switch to switch routing

[Zeleph25]

Implement switch-to-switch routing

What was added

This PR completes the routing pipeline so packets reach agents on any switch, not just the local one.

Proto changes:

• Add PacketAgentRegistered - switch reports an agent's virtual IP to the conductor
• Add PacketSwitchRouteUpdate - conductor broadcasts a route to all switches
• Add PacketSwitchDisconnected - conductor tells switches to drop routes for a disconnected switch
• Add AGENT_REGISTERED, SWITCH_ROUTE_UPDATE, SWITCH_DISCONNECTED to the packet type enum and dispatch

Conductor changes:

• onAgentRegistered - receives an agent's virtual IP from its switch, broadcasts it to all other switches
• Broadcasts SWITCH_DISCONNECTED to remaining switches when a switch disconnects
• Tracks assigned_switch per agent, nulled out safely when that switch disconnects

Switch changes:

• onSwitchRouteUpdate - connects to the peer switch if not already connected, updates the BlackBox routing table
• onSwitchDisconnected - closes the peer connection, letting onClose clean up routes
• onIPv4Raw - processes packets arriving from peer switches through the BlackBox and delivers them to the local agent
• Sends AGENT_REGISTERED to the conductor right after a new agent authenticates
• New PEER_SWITCH connection role with its own cleanup path in onClose

Verified:

[Switch] Connected to peer switch switch2
[Switch] Route update: 10.0.1.1 → switch2
[Conductor] Agent agent1 registered with IP 10.0.1.1 on switch switch2

Routes propagate correctly from the switch handling the agent to every other connected switch, with no conductor involvement once cached.