feat: add guest network autoconfiguration via Firecracker MMDS

Introduces optional per-clone IP assignment using the Firecracker Microvm
Metadata Service (MMDS). A background daemon (fc-net-init) is baked into
the rootfs during init and captured in the golden snapshot — on clone
resume it polls 169.254.169.254 and applies the IP/GW/DNS config injected
by the orchestrator immediately after snapshot restore.

- config.go: add AutoNetConfig bool (FC_AUTO_NET_CONFIG=1)
- orchestrator.go: embed fc-net-init daemon + MMDS link-local route in
  init script; set AllowMMDS: true on golden NIC; spawnOne/SpawnSingle
  accept net bool and propagate it via FC_AUTO_NET_CONFIG in proxy env
- console.go: set AllowMMDS: true on clone NIC; call configureMmds()
  after m.Start() when AutoNetConfig is enabled
- network.go: add configureMmds() — PUT /mmds with ip/gw/dns over the
  clone's Firecracker Unix socket
- serve.go: POST /clones accepts optional {"net": bool} body to override
  the global AutoNetConfig default per-request
- web/terminal.html: spawn button always sends {"net": true}
- docs/commands.md: document manual config + MMDS autoconfiguration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

orchestrator/console.go

@@ -88,6 +88,7 @@ func RunConsoleProxy(cfg Config, id int, tapName string) error {
 					MacAddress:  mac,
 					HostDevName: tapName,
 				},
+				AllowMMDS: true,
 			},
 		}
 	}
@@ -127,6 +128,17 @@ func RunConsoleProxy(cfg Config, id int, tapName string) error {
 	}
 	elapsed := time.Since(start)
 
+	// Inject per-clone IP config via MMDS so the fc-net-init guest daemon
+	// can configure eth0 without any manual steps inside the VM.
+	if cfg.AutoNetConfig && cfg.Bridge != "none" {
+		guestIP := fmt.Sprintf("%s.%d/24", cfg.GuestPrefix, 10+id)
+		if err := configureMmds(ctx, sockPath, guestIP, cfg.GuestGW, "1.1.1.1"); err != nil {
+			logger.Warnf("MMDS config failed (guest network will be unconfigured): %v", err)
+		} else {
+			logger.Infof("MMDS: assigned %s gw %s to clone %d", guestIP, cfg.GuestGW, id)
+		}
+	}
+
 	// Release our copy of the slave — firecracker holds its own fd now.
 	// Closing here ensures we get EOF on ptm when firecracker exits.
 	pts.Close()