Add developer build workflow

[joshbla]

Summary

• Add dependency files for running MaRMAT from source and building local packages.
• Add scripts for local setup, source execution, macOS packaging, and a packaged-app smoke test.
• Document the developer build workflow and ignore local build outputs, settings, and notes.

Test plan

• Ran ./scripts/setup-dev.sh successfully.
• Ran ./scripts/build-macos.sh successfully on macOS.
• Ran ./scripts/smoke-test-macos.sh successfully against the packaged app.