In `@app/javascript/controllers/stats_charts_controller.js`:
- Around line 16-19: The forEach callback in disconnect() implicitly returns
chart.destroy(), triggering the Biome lint rule; update the callback so it does
not return a value—either convert the arrow to a block body that calls
chart.destroy(); (i.e. use { chart.destroy(); }) or replace the forEach with an
explicit loop (for...of over this.charts) to call destroy on each chart, then
reset this.charts = [].

In `@app/javascript/helpers/object_helpers.js`:
- Around line 1-13: The deepMerge function exits early because the for...in loop
uses "return" when encountering inherited properties; change that "return" to
"continue" so the loop skips inherited keys without returning the whole
function. Also replace the unsafe obj2.hasOwnProperty(key) check with a safer
form such as Object.hasOwn(obj2, key) or
Object.prototype.hasOwnProperty.call(obj2, key) to avoid issues when obj2
shadows hasOwnProperty; keep the rest of deepMerge (result, recursion when
obj2[key] and obj1[key] are objects) unchanged.

In `@app/javascript/controllers/shot_charts_controller.js`:
- Around line 124-167: The button markup in setupInCupAnnotations is invalid (it
closes with </span>) and uses a static id "remove-annotations" which will
collide when multiple charts are on the page; fix by rendering a proper <button>
element (correct closing tag) via the chart.renderer call (or
renderer.createElement) and keep the returned element reference (e.g., save the
value returned from chart.renderer.text(...).add() or the created element)
instead of using document.getElementById; attach the click event to that element
reference, toggle annotation visibility using
chart.controller.destroyShotStages()/drawShotStages() and update the element's
label (use textContent) so each chart has its own independent control.
- Around line 29-48: The shotStagesNormalized mapping is assigning id: x (the
whole stage object) which breaks Highcharts' addPlotLine/removePlotLine that
expect a scalar id; change the mapping in initializeCharts (where
shotStagesNormalized is set) to use a stable scalar like id: x.value (or
String(x.value)) instead of the full object, and ensure any usage in
drawShotStages (and any code that calls
chart.xAxis[0].addPlotLine/removePlotLine) references that scalar id.

In `@app/javascript/controllers/shot_charts_controller.js`:
- Around line 221-225: In drawShotStages(), the inner forEach uses an arrow
expression that implicitly returns the result of addPlotLine (violates the lint
rule); change the callbacks to block bodies that call addPlotLine without
returning values — e.g., in drawShotStages replace
this.shotStagesNormalized.forEach(x => chart.xAxis[0].addPlotLine(x)) with
this.shotStagesNormalized.forEach(x => { chart.xAxis[0].addPlotLine(x); }) (and
similarly ensure the outer charts.forEach uses a block body if currently an
implicit return).
- Around line 152-175: The annotation toggle button created in
setupInCupAnnotations (chart.annotationButton / toggleButton) is left behind
when updateInCupVisibility removes annotations, causing duplicate buttons and
crashes; modify the code path in updateInCupVisibility to remove the button and
its listener when annotations are removed (e.g., if chart.annotationButton
exists call its destruction/removal and clear chart.annotationButton and
chart.annotationVisible), and harden the toggleButton click handler in
setupInCupAnnotations to guard before accessing chart.annotations[0] (check
chart.annotations && chart.annotations[0] && chart.annotations[0].graphic) so
the listener no-ops if annotations are missing. Ensure any added event listeners
are removed (or use a single attached handler) when the button is removed.