Fix grpc/rules_swift conflict for SparklePlugin build

- Downgrade grpc from 1.76.0.bcr.1 to 1.71.0
- Remove now-unnecessary rules_swift single_version_override

The issue: grpc 1.76.0+ depends on rules_swift 3.x, but rules_apple 4.x
requires rules_swift 2.x. These are different compatibility levels (3 vs 2),
causing a module resolution conflict that breaks the SparklePlugin build.

The fix: grpc 1.71.0 doesn't depend on rules_swift at all, cleanly avoiding
the conflict while still providing the gRPC functionality we need.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

MODULE.bazel

@@ -131,13 +131,6 @@ use_repo(
 
 bazel_dep(name = "apple_support", version = "1.21.1", repo_name = "build_bazel_apple_support")
 bazel_dep(name = "rules_apple", version = "4.3.3", repo_name = "build_bazel_rules_apple")
-# rules_swift is a transitive dep of rules_apple and grpc
-# grpc 1.76.0+ requires rules_swift 3.x, but rules_apple 4.x requires 2.x
-# Force version 3.1.2 since we don't use rules_swift directly
-single_version_override(
-    module_name = "rules_swift",
-    version = "3.1.2",
-)
 
 # Register Apple CC toolchain for Objective-C compilation
 apple_cc_configure = use_extension(
@@ -151,7 +144,10 @@ use_repo(apple_cc_configure, "local_config_apple_cc")
 #
 
 bazel_dep(name = "protobuf", version = "33.0", repo_name = "com_google_protobuf")
-bazel_dep(name = "grpc", version = "1.76.0.bcr.1")
+# grpc 1.71.0 instead of 1.76.0 to avoid rules_swift conflict
+# grpc 1.76.0+ depends on rules_swift 3.x, but rules_apple 4.x needs rules_swift 2.x
+# grpc 1.71.0 doesn't depend on rules_swift at all, avoiding the conflict
+bazel_dep(name = "grpc", version = "1.71.0")
 bazel_dep(name = "grpc-java", version = "1.71.0")
 bazel_dep(name = "flatbuffers", version = "25.9.23")