Release v1.2.0

• Automatic message truncation: messages exceeding Amazon's 256-character limit are automatically truncated to 253 characters + ... with warning logs, ensuring notifications are never dropped.
• In-memory anti-duplicate debounce filter: ignore identical consecutive notifications within a configurable time window (debounce_seconds, default: 0 / disabled) to prevent repeating alerts from bouncing sensors.
• Fix validation error handling: strip non-serializable exception objects from Pydantic error contexts to ensure validation failures return HTTP 422 instead of 500.
• Automated test suite: 20 unit tests with mocked Amazon APIs for fast and isolated verification.
• CI/CD workflow: GitHub Actions pipeline running test suite and validating Docker builds for both standalone and add-on images on every push and PR.