feat: --json output for rp flash deploy and dev

[lukepiette]

Summary

• Adds a --json flag to rp flash deploy and rp flash dev so agents and CI can consume a stable machine-readable contract instead of scraping rich-rendered text
• With --json, human-facing rich output moves to stderr and the final line of stdout is a JSON summary:
  • deploy → {"ok": true, "command": "deploy", "apps": [{"app", "env", "elapsed_s", "endpoints": {name: {"id", "url"}}}]}
  • deploy --build-only → {"ok": true, "command": "build", "artifacts": [{"app", "path", "size_bytes"}]}
  • dev --once → {"ok", "command": "dev", "module", "apps", "resources": [{"name", "kind", "hardware", "endpoint_id"}], "entrypoint": {"name", "ok", "elapsed_s", "error?"}}
  • failures → {"ok": false, "error": "..."} on stdout with the existing non-zero exit code
• dev --json requires --once (an interactive loop has no single summary to emit)

Test plan

• tests/test_cli/test_deploy_command.py — 10 new tests covering deploy/build/dev success, engine errors, discovery errors, multi-app, and the --json-requires---once guard
• Full tests/test_cli + tests/test_apps suites pass (606 passed)

🤖 Generated with Claude Code

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