Add minimal GitHub Actions CI and safety pattern checks

[monitorian]

Motivation

• Provide a minimal, non-privileged CI to catch syntactic and obvious unsafe changes before merge.
• Prevent accidental modification of hardware or timing behavior by statically flagging dangerous code patterns.
• Keep runtime and hardware control code untouched while enabling basic developer checks.

Description

• Add a GitHub Actions workflow at .github/workflows/ci.yml that runs on push to main and on pull_request with read-only contents permission and no elevated privileges.
• Add scripts/safety-checks.js, a static safety checker that scans source files and fails on while(true)/for(;;) infinite-loop patterns, setInterval calls below 1000 ms, and direct echonet-lite/hardware API usage outside approved wrapper files (and it excludes itself from scanning).
• Update package.json scripts to include lint, typecheck, build, and safety:check so CI runs npm run lint, npm run typecheck, npm run build, npm test, and npm run safety:check.
• CI scope: the pipeline validates syntax/lint, type/syntax gates, package build, tests, and the added dangerous-pattern detection; CI cannot validate actual hardware behavior, charging/electrical safety, or timing stability; end-to-end charging/ECHONET behavior and timing/retry/service behavior require real hardware testing.

Testing

• Ran npm run lint, npm run typecheck, npm run build, npm test, and npm run safety:check, and all of these commands completed successfully in the CI simulation.
• The workflow is configured to run the same steps on CI, so the added checks will execute automatically for push/pull_request events.

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Codex Task