Release v1.2.1

• Rollback debounce cache on delivery failure: if Amazon API or network fails, the message is unblocked so subsequent retries succeed immediately.
• Prevent startup crash (ValueError) when optional numeric environment variables are left empty in .env (DEFAULT_EXPIRY_HOURS="", DEBOUNCE_SECONDS="").
• Concurrency protection: thread-safe asyncio.Lock in TokenCache to prevent duplicate OAuth2 token requests during concurrent notifications.
• Validation hardening: reject NaN and Infinity values in Pydantic models (allow_inf_nan=False).
• Memory bound in DebounceFilter: enforce _max_entries limit by pruning oldest entry when the cache is full.
• Home Assistant Watchdog: enable native HA supervisor watchdog monitoring on /health endpoint.
• Add-on schema alignment: adjust minimum default_expiry_hours to 0.1 (6 min) to prevent out-of-bounds warnings on startup.
• Robust Bashio parsing: use bashio::config.has_value in run.sh to prevent empty fields exporting literal "null" strings.
• Pure Python Uvicorn: switch to uvicorn (without [standard] C-extensions) to ensure reliable multi-arch builds on Alpine Linux (armv7/armhf).
• CI/CD synchronization check: automated CI check ensuring standalone and add-on files remain strictly identical.