Add Android process finder interface for per-app routing (#182)

* Initial plan

* Add Android process finder interface for per-app routing

Agent-Logs-Url: https://github.com/2dust/AndroidLibXrayLite/sessions/319cba61-5c38-403c-bec5-3f01d1fd70c2

Co-authored-by: 2dust <31833384+2dust@users.noreply.github.com>

* Update README.md

* Add panic recovery to Android process finder callback

Change the registered Android process finder callback to use named return values and add a defer/recover block that converts panics into a formatted error. This prevents panics in the Finder implementation from propagating into corenet and improves robustness while preserving the existing "process not found" error behavior.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: 2dust <31833384+2dust@users.noreply.github.com>

android_process_finder.go

@@ -0,0 +1,48 @@
+//go:build android
+
+package libv2ray
+
+import (
+	"fmt"
+
+	corenet "github.com/xtls/xray-core/common/net"
+)
+
+// ProcessFinder is an interface for Android process finding functionality.
+// Apps using AndroidLibXrayLite should implement FindProcessByConnection()
+// and pass the implementation to RegisterProcessFinder() before starting the core.
+type ProcessFinder interface {
+	// FindProcessByConnection finds the UID of the process that owns the given connection.
+	//
+	// network: Protocol type: "tcp" or "udp"
+	// srcIP: Source IP address
+	// srcPort: Source port
+	// destIP: Destination IP address
+	// destPort: Destination port
+	// Returns the UID of the owning process, or -1 if not found.
+	FindProcessByConnection(network, srcIP string, srcPort int, destIP string, destPort int) int
+}
+
+// RegisterProcessFinder registers an Android process finder with Xray-core,
+// enabling per-app routing based on UID. Must be called before starting the
+// core for process-based routing rules to work.
+// Pass nil to unregister a previously registered finder.
+func RegisterProcessFinder(finder ProcessFinder) {
+	if finder == nil {
+		corenet.RegisterAndroidProcessFinder(nil)
+		return
+	}
+
+	corenet.RegisterAndroidProcessFinder(func(network, srcIP string, srcPort uint16, destIP string, destPort uint16) (uid int, name string, path string, err error) {
+		defer func() {
+			if r := recover(); r != nil {
+				uid, name, path, err = 0, "", "", fmt.Errorf("process finder panic: %v", r)
+			}
+		}()
+		uid = finder.FindProcessByConnection(network, srcIP, int(srcPort), destIP, int(destPort))
+		if uid < 0 {
+			return 0, "", "", fmt.Errorf("process not found for %s %s:%d -> %s:%d", network, srcIP, srcPort, destIP, destPort)
+		}
+		return uid, fmt.Sprintf("%d", uid), "", nil
+	})
+}