Report live Bazel progress to build proxies

[karim-alweheshy]

Summary

• request Bazel's one-second progress-report cadence only for build-proxy invocations
• keep that presentation-only option out of metadata replay and publishable invocation receipts
• add source-level coverage for proxy and non-proxy command construction

Stack

• Base: Declare generated Bazel environment keys #3334
• Paired proxy slices: Surface live Bazel progress in Xcode karim-alweheshy/XCBBuildServiceProxyKit#16 and Allow production-scale Bazel output karim-alweheshy/XCBBuildServiceProxyKit#17

Validation

• focused launcher Bazel test passed uncached with --ignore_all_rc_files
• bash -n, scoped ShellCheck, Buildifier, and TruffleHog passed
• generated RedditApp adapter contains --progress_report_interval=1
• Xcode 26.5 RedditApp build succeeded while displaying changing current activity and estimated completed/total counts

Testing

Generate a project with a build proxy, inspect the generated adapter for the proxy-only progress option, then build from Xcode and confirm the activity view changes at the requested cadence. Generate without a proxy and confirm the option is absent.