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"
   }
+}
 ];

desktop/angular/src/app/shared/netquery/connection-details/conn-details.html

@@ -255,6 +255,17 @@
     </ng-container>
   </div>
 
+  <div *ngIf="!!conn.extra_data?.split_tun">
+    <h3 class="text-primary text-xxs">Split Tunnel</h3>
+    <div *ngIf="conn.extra_data?.split_tun as splitTun" class="meta">
+      <span class="inline-flex items-center gap-1 flex-wrap">
+        <span class="text-secondary">This connection is forcibly routed through interface</span>
+        <span>{{ splitTun.Interface }}</span>
+        <span class="text-secondary">({{ splitTun.IP }})</span>
+      </span>      
+    </div>
+  </div>
+
   <div *ngIf="!!bwData.length" class="col-span-3 block border-t border-gray-400 py-2">
     <h2 class="text-secondary uppercase w-full text-center text-xxs">Data Usage</h2>
     <sfng-netquery-line-chart class="block w-full !h-36" [data]="bwData" [config]="{