- Introduced `c_arm_relaxed` to the CircumferenceEntry model for tracking relaxed arm measurements.
- Updated database schema to include `c_arm_relaxed` in the circumference_log table.
- Implemented calculation for 28-day relaxed arm circumference change with `calculate_arm_relaxed_28d_delta`.
- Enhanced placeholder resolver and registration to support new relaxed arm measurement.
- Updated frontend components to accommodate the new measurement, including forms and CSV exports.
- Improved documentation and guide data to reflect the addition of relaxed arm measurements.
