feat(fitness/stats): 4 cm minimum y-axis range on body-part history charts

Body-measurement variation of <4 cm used to stretch the full chart
height, making normal weekly noise look dramatic. Now the y-axis
enforces a 4 cm floor centered on the data's midpoint; wider swings
render at their actual range as before.

- FitnessChart: new optional `yMin` / `yMax` props mapped to Chart.js
  `suggestedMin` / `suggestedMax` — soft bounds, so data that exceeds
  them still widens the axis.
- `/fitness/stats/history/[part]`: computes min/max across available
  values (both sides if paired), enforces the 4 cm floor, passes to
  FitnessChart. Tick distance stays on Chart.js auto — small ranges
  get 0.5 cm ticks, wider ones scale up naturally.

TODO.md

@@ -7,7 +7,7 @@
 [x] add a button on /fitness/measure/body-parts for each measurement directly below to say "Same value", instead of having to hit +, then - to lock in same number
 [x] BF graph (with trend line like weight graph) on /fitness/stats page. Emphasize relative changes, not absolute numbers in design (as we cannot trust those) (e.g., use start day of overview as 0% and then show +/- x % on the graph)
 [x] Workshop better names than "Measure" for the /fitness/measure route. It's about body data points (i.e., non-food related). What's a better, short name than "Measure" to capture the logging of weight, body composition, body part measurements, and period tracking?
-[ ] on /fitness/stats/histoy/<part> for body measurement graphs, make the range reasonable. e.g., if we have 1 cm change, do not fill the entire y-height with 1 cm. Use reasonable padding for low ranges (i think we do something like htis already on the weight graph?)
+[x] on /fitness/stats/histoy/<part> for body measurement graphs, make the range reasonable. e.g., if we have 1 cm change, do not fill the entire y-height with 1 cm. Use reasonable padding for low ranges (i think we do something like htis already on the weight graph?)
 
 ## Refactor Recipe Search Component
 

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.46.8",
+	"version": "1.46.9",
 	"private": true,
 	"type": "module",
 	"scripts": {

src/lib/components/fitness/FitnessChart.svelte

@@ -11,10 +11,12 @@
 	 *   height?: string,
 	 *   yUnit?: string,
 	 *   goalLine?: number,
-	 *   tooltipFormatter?: (value: number, datasetIndex: number, dataIndex: number, label: string) => string
+	 *   tooltipFormatter?: (value: number, datasetIndex: number, dataIndex: number, label: string) => string,
+	 *   yMin?: number,
+	 *   yMax?: number
 	 * }}
 	 */
-	let { type = 'line', data, title = '', height = '250px', yUnit = '', goalLine = undefined, tooltipFormatter = undefined } = $props();
+	let { type = 'line', data, title = '', height = '250px', yUnit = '', goalLine = undefined, tooltipFormatter = undefined, yMin = undefined, yMax = undefined } = $props();
 
 	/** @type {HTMLCanvasElement | undefined} */
 	let canvas = $state(undefined);
@@ -125,6 +127,8 @@
 					},
 					y: {
 						beginAtZero: type === 'bar',
+						suggestedMin: yMin,
+						suggestedMax: yMax,
 						grid: { color: gridColor },
 						border: { display: false },
 						ticks: {

src/routes/fitness/[stats=fitnessStats]/[history=fitnessHistory]/[part]/+page.svelte

@@ -84,6 +84,24 @@
 		};
 	});
 
+	/**
+	 * Enforce a minimum y-axis range of 4 cm — prevents tiny variations
+	 * from stretching across the full chart height.
+	 */
+	const Y_MIN_RANGE = 4;
+	const yRange = $derived.by(() => {
+		/** @type {number[]} */
+		const vals = series.paired
+			? [...series.left, ...series.right].filter((/** @type {number|null} */ v) => v != null)
+			: series.values.filter((/** @type {number|null} */ v) => v != null);
+		if (vals.length === 0) return { min: undefined, max: undefined };
+		const dMin = Math.min(...vals);
+		const dMax = Math.max(...vals);
+		if (dMax - dMin >= Y_MIN_RANGE) return { min: dMin, max: dMax };
+		const mid = (dMin + dMax) / 2;
+		return { min: mid - Y_MIN_RANGE / 2, max: mid + Y_MIN_RANGE / 2 };
+	});
+
 	/**
 	 * @typedef {{ paired: true, latest: { left: number|null, right: number|null }, first: { left: number|null, right: number|null }, count: number }} PairedStats
 	 * @typedef {{ paired: false, latest: number|null, first: number|null, count: number, min: number|null, max: number|null }} SingleStats
@@ -230,7 +248,7 @@
 		</section>
 
 		<section class="chart-wrap">
-			<FitnessChart data={chartData} yUnit=" cm" height="320px" />
+			<FitnessChart data={chartData} yUnit=" cm" height="320px" yMin={yRange.min} yMax={yRange.max} />
 		</section>
 	{/if}
 </div>