feat: Add Split Tunnel feature (Windows PoC)

Implement initial proof-of-concept for split tunnel functionality on Windows,
allowing applications to route traffic through a designated network interface
while bypassing default system routing.

Features:
- Split tunnel module with TCP/UDP proxy infrastructure
- Firewall integration with split tunnel verdict handling
- SplitTunneling context attached to connections
- Configuration options: enable toggle, interface selection, and policy rules
- UI display of split tunnel connection details in connection info panel
- Subsystem configuration for user-level access

Windows-specific implementation:
- Uses proxy-based interface routing on Windows
- Automatic or manual interface detection and binding
- Support for IPv4 and IPv6 traffic

Note: Linux implementation is under development. SPN takes precedence over
split tunnel when both are enabled, ensuring SPN connections bypass this feature.

desktop/angular/src/app/shared/config/config-settings.ts

@@ -427,11 +427,16 @@ export class ConfigSettingsViewComponent
                   (s) => s.Key === subsys.ToggleOptionKey
                 );
                 if (!!toggleOption) {
-                  if (
-                    (toggleOption.Value !== undefined && !toggleOption.Value) ||
-                    (toggleOption.Value === undefined &&
-                      !toggleOption.DefaultValue)
-                  ) {
+                  // Determine the effective enabled state: per-app value takes
+                  // priority, then the globally-configured value (GlobalDefault),
+                  // and finally the hardcoded DefaultValue.
+                  const effectiveEnabled =
+                    toggleOption.Value !== undefined
+                      ? !!toggleOption.Value
+                      : toggleOption.GlobalDefault !== undefined
+                        ? !!toggleOption.GlobalDefault
+                        : !!toggleOption.DefaultValue;
+                  if (!effectiveEnabled) {
                     subsys.isDisabled = true;
 
                     // remove all settings for all subsystem categories

desktop/angular/src/app/shared/config/subsystems.ts

@@ -7,7 +7,7 @@ export interface SubsystemWithExpertise extends Subsystem {
   hasUserDefinedValues: boolean;
 }
 
-export var subsystems : SubsystemWithExpertise[] = [
+export const subsystems : SubsystemWithExpertise[] = [
   {
     minimumExpertise: ExpertiseLevelNumber.developer,
     isDisabled: false,
@@ -268,5 +268,30 @@ export var subsystems : SubsystemWithExpertise[] = [
       Deleted: 0,
       Key: "runtime:subsystems/spn"
     }
+  },
+  {
+  minimumExpertise: ExpertiseLevelNumber.user,  // User level since UI is user-facing
+  isDisabled: false,
+  hasUserDefinedValues: false,
+  ID: "splittun",
+  Name: "Split Tunnel",
+  Description: "Route traffic through specified interface to bypass default routing",
+  Modules: [
+    {
+      Name: "splittun",
+      Enabled: true
+    }
+  ],
+  ToggleOptionKey: "splittun/use",  // Links to the boolean enable/disable option
+  ExpertiseLevel: "user",
+  ReleaseLevel: 0,
+  ConfigKeySpace: "config:splittun/",
+  _meta: {
+    Created: 0,
+    Modified: 0,
+    Expires: 0,
+    Deleted: 0,
+    Key: "runtime:subsystems/splittun"
   }
+}
 ];