refactor: code quality, logging and reliability improvements

[Kannix2005]

Critical fixes:

• Replace bare except clauses with specific exceptions throughout
• Fix hass.bus.fire() called from FCM thread → call_soon_threadsafe + async_fire
• Guard e.response None-check before accessing .status_code in all HTTP methods
• Save FCM credentials with 0o600 permissions instead of world-readable defaults

Logging cleanup:

• Standardise all _LOGGER calls to %-style format (no f-strings)
• Demote verbose SIP connect/register steps from INFO to DEBUG
• Demote FCM registration details, listener lifecycle, MQTT messages to DEBUG
• Remove traceback duplication (use _LOGGER.exception instead of error+format_exc)
• Mask FCM tokens in log output

Architecture:

• SiedleDataUpdateCoordinator now holds direct ConfigEntry reference; removes O(n) loop over hass.data to find its own entry on every coordinator update
• binary_sensor.py: replace hardcoded "Siedle Türstation" device name with endpoint_id-based name, matching sensor.py convention
• Add SIEDLE_DATA_DIR and TASK_NAME_FCM_SETUP constants to replace magic strings

Reliability:

• MQTT connect_mqtt() retries up to 3 times with exponential backoff (1s, 2s) and enables paho auto-reconnect (1–30s) for post-connect drops