build(api): expose RPC proto sources

Summary:
Intent:
- Allow downstream Bazel repositories to vendor published RPC contracts directly.

Changes:
- Make the Runway, Stovepipe, SubmitQueue gateway, and SubmitQueue orchestrator proto sources publicly visible.

---

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Author: mnoah1

api/runway/proto/BUILD.bazel

@@ -1,4 +1,4 @@
 exports_files(
     ["runway.proto"],
-    visibility = ["//tool/proto:__pkg__"],
+    visibility = ["//visibility:public"],
 )

api/stovepipe/proto/BUILD.bazel

@@ -1,4 +1,4 @@
 exports_files(
     ["stovepipe.proto"],
-    visibility = ["//tool/proto:__pkg__"],
+    visibility = ["//visibility:public"],
 )

api/submitqueue/gateway/proto/BUILD.bazel

@@ -1,4 +1,4 @@
 exports_files(
     ["gateway.proto"],
-    visibility = ["//tool/proto:__pkg__"],
+    visibility = ["//visibility:public"],
 )

api/submitqueue/orchestrator/proto/BUILD.bazel

@@ -1,4 +1,4 @@
 exports_files(
     ["orchestrator.proto"],
-    visibility = ["//tool/proto:__pkg__"],
+    visibility = ["//visibility:public"],
 )