perf(build): speed up local CLI rebuilds

[johntmyers]

Summary

Speeds up local OpenShell CLI rebuilds by removing avoidable build invalidation and expensive protobuf compilation work from the dev path.

Related Issue

N/A

Changes

• Removed protobuf-src so openshell-core no longer compiles the C++ protobuf library from source during local builds.
• Updated protobuf codegen to use protoc from PATH, with a mise fallback for direct cargo usage.
• Stopped watching .git/HEAD and .git/refs/tags in the core build script so commits, checkouts, and branch switches do not cascade a full CLI rebuild.
• Added [profile.dev.build-override] opt-level = 2 so build scripts and proc macros run optimized after their first compile.
• Updated Docker build images that compile Rust crates directly to install protobuf-compiler now that protobuf-src is gone.
• Updated the local scripts/bin/openshell wrapper to disable RUSTC_WRAPPER by default for faster iterative rebuilds; set OPENSHELL_CLI_USE_SCCACHE=1 to opt back into sccache.
• Fixed plaintext HTTP gateway health checks so macOS dev builds do not require native root CA loading for http:// endpoints.

Testing

• RUSTC_WRAPPER= cargo check -p openshell-core
• RUSTC_WRAPPER= cargo test -p openshell-cli http_health_check_supports_plain_http_endpoints -- --nocapture
• scripts/bin/openshell --help repeat invocation after rebuild completed in ~0.2s locally
• mise run pre-commit

Checklist

• Tests added or updated where appropriate
• Documentation updated where appropriate
• Security considerations reviewed