fix(fptn): add fptn action to sing-box route target and outbound generation

- Add fptn to route.target() to prevent exit(2) crash on config generation
- Add add_fptn_outbound() using direct outbound with routing_mark=0x00300000
  (routes traffic through tun-fptn via kernel ip rule → table 4249)
- Add fptn to reserve_section_outbound_tags
- Add fptn to generator_routes outbound dispatch

Fixes torrents and all traffic breaking when an FPTN section is configured.

tachyon/files/usr/lib/singbox/generator_outbounds.uc

@@ -1844,6 +1844,16 @@ function add_olcrtc_outbound(config, section, sections) {
     });
 }
 
+// FPTN routes traffic through its TUN interface (tun-fptn) via kernel routing.
+// fwmark 0x00300000 (3145728) → ip rule → routing table 4249 → dev tun-fptn.
+function add_fptn_outbound(config, section, sections) {
+    push(config.outbounds, {
+        type: "direct",
+        tag: outbound_tag(section[".name"]),
+        routing_mark: 3145728
+    });
+}
+
 return {
     init,
     reserved_runtime_tag_set,
@@ -1880,5 +1890,6 @@ return {
     add_zapret2_outbound,
     add_byedpi_outbound,
     add_wdtt_outbound,
-    add_olcrtc_outbound
+    add_olcrtc_outbound,
+    add_fptn_outbound
 };

tachyon/files/usr/lib/singbox/generator_routes.uc

@@ -1824,6 +1824,8 @@ function add_outbound_for_section(config, section, taken, sections) {
         ctx.outbounds.add_wdtt_outbound(config, section, sections);
     else if (action == "olcrtc")
         ctx.outbounds.add_olcrtc_outbound(config, section, sections);
+    else if (action == "fptn")
+        ctx.outbounds.add_fptn_outbound(config, section, sections);
     else if (action == "bypass") {
         /* route-only action */
     }
@@ -1849,7 +1851,7 @@ function reserve_section_outbound_tags(sections, taken) {
         let action = option(section, "action", "");
         if (connections.is_connections_action(action) ||
             action == "awg" || action == "warp" || action == "byedpi" || action == "zapret" || action == "zapret2" ||
-            action == "wdtt" || action == "olcrtc" ||
+            action == "wdtt" || action == "olcrtc" || action == "fptn" ||
             action == "anytls" || action == "snell" || action == "mieru" || action == "sudoku" ||
             action == "masque" || action == "openvpn")
             taken[outbound_tag(section[".name"])] = true;

tachyon/files/usr/lib/singbox/route.uc

@@ -126,7 +126,7 @@ function target(section, outbound_tag_name) {
         action == "anytls" || action == "snell" || action == "mieru" || action == "sudoku" ||
         action == "masque" || action == "openvpn" ||
         action == "byedpi" || action == "zapret" || action == "zapret2" ||
-        action == "wdtt" || action == "olcrtc")
+        action == "wdtt" || action == "olcrtc" || action == "fptn")
         return { action: "route", outbound: outbound_tag_name };
     if (action == "bypass")
         return { action: "route", outbound: runtime_constants.BYPASS_OUTBOUND_TAG };