Support custom outbound tags in routing

Allow routing rules to reference outbounds by server remarks and inject missing outbounds into the generated V2ray config. Adds BUILTIN_OUTBOUND_TAGS, a pre-pass (injectCustomOutbounds) that converts referenced non-builtin tags to outbounds, and a fallback to the proxy tag when an outbound couldn't be injected. Updates getBalance to use AppConfig.TAG_PROXY constant. Replaces the outbound-tag Spinner with an AutoCompleteTextView + dropdown button that suggests builtin tags and existing profile remarks, adds a drop-down drawable and a hint string resource.

V2rayNG/app/src/main/res/values/strings.xml

@@ -342,6 +342,7 @@
     <string name="routing_settings_protocol_tip">[http,tls,bittorrent]</string>
     <string name="routing_settings_network">network</string>
     <string name="routing_settings_network_tip">[udp|tcp]</string>
+    <string name="routing_settings_outbound_tag_hint" translatable="false">proxy / direct / block / &lt;remarks&gt;</string>
     <string name="routing_settings_outbound_tag">outboundTag</string>
 
     <string name="connection_test_pending">Check Connectivity</string>