step 7: harden docs and prepare beta

docs/API_REFERENCE.md

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+# API Reference
+
+## Configuration
+
+- `configure(**config)`: set package-wide defaults for later gauges.
+
+## Gauge Creation
+
+Creation functions are context managers and accept common options such as `tag`, `label`, `value`,
+`min_value`, `max_value`, `unit`, `width`, `height`, `show`, `tooltip`, `callback`, `theme`,
+`style`, `animation`, `smoothing`, `thresholds`, and `markers`.
+
+- `analog_gauge(**config)`
+- `digital_gauge(**config)`
+- `bar_gauge(**config)`
+- `level_gauge(**config)`
+- `status_light(**config)`
+- `segmented_gauge(**config)`
+- `compass_gauge(**config)`
+- `thermometer_gauge(**config)`
+- `battery_gauge(**config)`
+- `multi_value_gauge(**config)`
+
+## Layout Helpers
+
+- `gauge_panel(**config)`: child-window panel for grouped gauges.
+- `gauge_grid(**config)`: lightweight horizontal gauge group.
+
+## Runtime API
+
+- `set_value(tag, value)`: set the latest target value.
+- `get_value(tag)`: return the latest raw target value.
+- `update_gauge(tag, **config)`: update value and/or configuration.
+- `configure_gauge(tag, **config)`: update configuration.
+- `set_thresholds(tag, thresholds)`: replace visual threshold bands.
+- `set_markers(tag, markers)`: replace visual markers.
+- `set_show(tag, show)`: show or hide a gauge.
+- `delete_gauge(tag)`: remove a gauge.
+- `get_gauge_debug_state(tag)`: return internal debug state.
+
+Runtime functions are GUI-thread functions unless explicitly documented otherwise.