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/internal/utils/version.go

@@ -33,6 +33,12 @@ func IsNewerVersion(version1, version2 string) bool {
 	return CompareVersions(version1, version2) == 1
 }
 
+// IsNewerOrEqualVersion returns true if version1 is newer than or equal to version2
+func IsNewerOrEqualVersion(version1, version2 string) bool {
+	cmp := CompareVersions(version1, version2)
+	return cmp == 1 || cmp == 0
+}
+
 // parseVersion parses a version string like "0.1.4" into [0, 1, 4]
 func parseVersion(version string) [3]int {
 	// Default version if parsing fails