Stabilize Fusion builds and simplify optional modules.

Fix Fusion defaults and icon handling, remove unsupported UI fields, and ensure server/web/agent builds and tests pass cleanly on Windows.

server/internal/sys/firewall_stub.go

@@ -0,0 +1,9 @@
+//go:build !windows
+
+package sys
+
+import "fmt"
+
+func EnsureInboundTCPPort(port int, ruleName string) error {
+	return fmt.Errorf("automatic firewall rules are only supported on Windows")
+}