fitness: add cardio kcal estimation with Minetti/Ainsworth models

Add cardioKcalEstimate.ts implementing tiered calorie estimation for
cardio exercises: Minetti gradient-dependent polynomials for GPS
run/walk/hike, cycling physics model, MET-based fallbacks from
Ainsworth Compendium, and flat-rate estimates. Wire cardio kcal into
SessionCard, workout completion screen, history detail, and stats
overview API alongside existing strength kcal (Lytle). Move citation
info from stats overview to clickable DOI links on workout detail
kcal pill.

src/routes/fitness/[workout=fitnessWorkout]/[active=fitnessActive]/+page.svelte

@@ -10,6 +10,7 @@
 	import { getWorkoutSync } from '$lib/js/workoutSync.svelte';
 	import { getExerciseById, getExerciseMetrics } from '$lib/data/exercises';
 	import { estimateWorkoutKcal } from '$lib/data/kcalEstimate';
+	import { estimateCardioKcal } from '$lib/data/cardioKcalEstimate';
 	import ExerciseName from '$lib/components/fitness/ExerciseName.svelte';
 	import SetTable from '$lib/components/fitness/SetTable.svelte';
 	import ExercisePicker from '$lib/components/fitness/ExercisePicker.svelte';
@@ -193,13 +194,32 @@
 			};
 		});
 
-		// Estimate kcal for strength exercises
+		// Estimate kcal for strength + cardio exercises
 		/** @type {import('$lib/data/kcalEstimate').ExerciseData[]} */
 		const kcalExercises = [];
+		let cardioKcal = 0;
+		let cardioMarginSq = 0;
 		for (const ex of local.exercises) {
 			const exercise = getExerciseById(ex.exerciseId, lang);
 			const metrics = getExerciseMetrics(exercise);
-			if (metrics.includes('distance')) continue;
+			if (metrics.includes('distance')) {
+				let dist = 0;
+				let dur = 0;
+				for (const s of ex.sets) {
+					if (!s.completed) continue;
+					dist += s.distance ?? 0;
+					dur += s.duration ?? 0;
+				}
+				if (dist > 0 || dur > 0) {
+					const r = estimateCardioKcal(ex.exerciseId, 80, {
+						distanceKm: dist || undefined,
+						durationMin: dur || undefined,
+					});
+					cardioKcal += r.kcal;
+					cardioMarginSq += (r.kcal - r.lower) ** 2;
+				}
+				continue;
+			}
 			const weightMultiplier = exercise?.bilateral ? 2 : 1;
 			const sets = ex.sets
 				.filter((/** @type {any} */ s) => s.completed && s.reps > 0)
@@ -209,7 +229,18 @@
 				}));
 			if (sets.length > 0) kcalExercises.push({ exerciseId: ex.exerciseId, sets });
 		}
-		const kcalResult = kcalExercises.length > 0 ? estimateWorkoutKcal(kcalExercises) : null;
+		const strengthResult = kcalExercises.length > 0 ? estimateWorkoutKcal(kcalExercises) : null;
+		let kcalResult = null;
+		if (strengthResult || cardioKcal > 0) {
+			const total = (strengthResult?.kcal ?? 0) + cardioKcal;
+			const sMargin = strengthResult ? (strengthResult.kcal - strengthResult.lower) : 0;
+			const margin = Math.round(Math.sqrt(sMargin ** 2 + cardioMarginSq));
+			kcalResult = {
+				kcal: Math.round(total),
+				lower: Math.max(0, Math.round(total) - margin),
+				upper: Math.round(total) + margin,
+			};
+		}
 
 		return {
 			sessionId: saved._id,