feat: Add per-app proxy (Split Tunneling) for desktop platforms

- Add PerAppProxyOptions struct with Mode, IncludedApplications, ExcludedApplications
- Implement routing rules for include/exclude modes
- Include mode: selected apps use VPN, others go direct
- Exclude mode: selected apps bypass VPN, others use VPN
- Only active on non-Android platforms (Windows, Linux, macOS)
- Logging added for debugging per-app routing decisions

Part of v1.7.6 Split Tunneling feature

config/hiddify_option.go

@@ -26,6 +26,13 @@ type HiddifyOptions struct {
 	InboundOptions
 	URLTestOptions
 	RouteOptions
+	PerAppProxyOptions
+}
+
+type PerAppProxyOptions struct {
+	Mode                 string   `json:"per-app-proxy-mode"`        // "off", "include", "exclude"
+	IncludedApplications []string `json:"included-applications"`     // ["chrome.exe", "firefox.exe"]
+	ExcludedApplications []string `json:"excluded-applications"`     // ["steam.exe", "uTorrent.exe"]
 }
 
 type DNSOptions struct {