Declare generated Bazel environment keys

[karim-alweheshy]

Summary

• Publish the names of generated Bazel environment entries in the proxy manifest.
• Sort and validate names deterministically.
• Reject invalid and credential-shaped names; no environment values are published.

Stack

• Depends on the bounded BEP PR.
• Pairs with XCBBuildServiceProxyKit fork PR Don't return PBXProject from createProject() #14.

Validation

• Manifest unit test passed uncached.
• Buildifier and diff checks passed.
• RedditApp manifest declares its custom Bazel environment names, the receipt validates, and Xcode reports Build succeeded.

Testing

Run bazel --ignore_all_rc_files test //test/internal/build_proxy_manifest:build_proxy_manifest_tests.

Follow-up validation

• Reproduced the integration failure as an argparse positional/option intermixing bug.
• Added a CLI regression with an environment option before a real manifest fragment.
• Bazel 8.7 and 9.2 focused tests pass uncached.
• The exact examples/integration project-generation command succeeds locally after changing only the repository’s Xcode 26.1.1 transition to the installed Xcode 26.5 as a local test control; that transition change is not committed.
• The subsequent //... build reached platform compilation and stopped only because this host has no tvOS Simulator runtime; this is independent of the manifest action.