feat: switch orchestrator from Fargate to EC2 Spot

Dispatcher now launches Spot instances instead of Fargate tasks:
- t3.small for go/node builds ($0.005/hr)
- t3.medium for docker/godot builds ($0.01/hr)
- t3.micro for deploy jobs ($0.004/hr)

Instances self-terminate via user-data trap on exit.
Cancel: ec2:TerminateInstances instead of ecs:StopTask.
Cleanup cron also sweeps orphan instances by tinqs-ci tag.

Pre-baked AMI with act_runner + tools = instant boot, no install.

orchestrator/dispatch/go.mod

@@ -8,7 +8,7 @@ require (
 	github.com/aws/aws-sdk-go-v2/config v1.28.0
 	github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue v1.15.12
 	github.com/aws/aws-sdk-go-v2/service/dynamodb v1.38.0
-	github.com/aws/aws-sdk-go-v2/service/ecs v1.52.0
+	github.com/aws/aws-sdk-go-v2/service/ec2 v1.198.0
 	github.com/aws/aws-sdk-go-v2/service/lambda v1.69.0
 	gopkg.in/yaml.v3 v3.0.1
 )