Implement sensor auto-discovery feature

New Features:
- Automatic discovery of unknown Bluetooth sensors
- Discovery manager tracks pending/approved/ignored sensors
- ntfy notifications when new sensors found (optional)
- Interactive CLI tool: sensorpajen-approve-sensors
- Automatic config reload every 15 minutes (no restart needed)

Files Added:
- src/sensorpajen/discovery_manager.py: Sensor discovery management
- src/sensorpajen/approve_sensors.py: Interactive approval CLI
- config/discovered_sensors.json.example: Example discovery file

Files Modified:
- src/sensorpajen/config.py: Added ntfy and discovery config
- src/sensorpajen/main.py: Added discovery manager and config reload
- src/sensorpajen/sensor_reader.py: Added discovery on unknown sensors
- config/sensorpajen.env.example: Added ntfy and reload settings
- pyproject.toml: Added approve-sensors CLI command

Configuration:
- NTFY_ENABLED, NTFY_URL, NTFY_TOPIC, NTFY_TOKEN
- DISCOVERED_SENSORS_FILE, CONFIG_RELOAD_INTERVAL
- Pre-filled comments with sensor metadata

See TASKS.md for complete feature specification.

pyproject.toml

@@ -44,6 +44,7 @@ Repository = "https://github.com/yourusername/sensorpajen"
 
 [project.scripts]
 sensorpajen = "sensorpajen.main:main"
+sensorpajen-approve-sensors = "sensorpajen.approve_sensors:main"
 
 [tool.setuptools.packages.find]
 where = ["src"]