feat: machine binding and version enforcement

migration 017 adds machine_id to agents table
middleware validates X-Machine-ID header on authed routes
agent client sends machine ID with requests
MIN_AGENT_VERSION config defaults 0.1.22
version utils added for comparison

blocks config copying attacks via hardware fingerprint
old agents get 426 upgrade required
breaking: <0.1.22 agents rejected

aggregator-server/go.mod

@@ -7,9 +7,8 @@ require (
 	github.com/golang-jwt/jwt/v5 v5.3.0
 	github.com/google/uuid v1.6.0
 	github.com/jmoiron/sqlx v1.4.0
-	github.com/joho/godotenv v1.5.1
 	github.com/lib/pq v1.10.9
-	golang.org/x/term v0.33.0
+	golang.org/x/crypto v0.40.0
 )
 
 require (
@@ -36,7 +35,6 @@ require (
 	github.com/ugorji/go/codec v1.3.0 // indirect
 	go.uber.org/mock v0.5.0 // indirect
 	golang.org/x/arch v0.20.0 // indirect
-	golang.org/x/crypto v0.40.0 // indirect
 	golang.org/x/mod v0.25.0 // indirect
 	golang.org/x/net v0.42.0 // indirect
 	golang.org/x/sync v0.16.0 // indirect