fix(06-02): improve mobile muscle list layout and grouping

- Issue 1: Two-line layout per muscle (name+ratio on line 1, progress bar on line 2)
- Issue 2: Remove set totals from group headers (show group name + chevron only)
- Issue 3: Merge Forearms into Arms group (reduce from 7 to 6 UI groups)

Changes:
- src/core/taxonomy.ts: Move Forearm muscles into Arms group, remove Forearms from UIMuscleGroup type
- src/ui/components/mobile/MobileMuscleList.tsx: Two-line muscle layout with h-1 progress bar, remove group summary display

Author: pineapplestrikesback

src/core/taxonomy.ts

@@ -171,7 +171,7 @@ export type ExerciseMapping = Partial<Record<ScientificMuscle, number>>;
  * UI muscle group categories for displaying muscles in forms/editors.
  * This is the single source of truth for UI components like MuscleValueEditor.
  */
-export type UIMuscleGroup = 'Back' | 'Chest' | 'Shoulders' | 'Arms' | 'Legs' | 'Core' | 'Forearms';
+export type UIMuscleGroup = 'Back' | 'Chest' | 'Shoulders' | 'Arms' | 'Legs' | 'Core';
 
 /**
  * UI muscle groups with their constituent ScientificMuscles.
@@ -209,6 +209,8 @@ export const UI_MUSCLE_GROUPS: readonly { name: UIMuscleGroup; muscles: readonly
       'Biceps Brachii',
       'Triceps (Long Head)',
       'Triceps (Lateral/Medial)',
+      'Forearm Flexors',
+      'Forearm Extensors',
     ],
   },
   {
@@ -232,11 +234,4 @@ export const UI_MUSCLE_GROUPS: readonly { name: UIMuscleGroup; muscles: readonly
       'Hip Flexors',
     ],
   },
-  {
-    name: 'Forearms',
-    muscles: [
-      'Forearm Flexors',
-      'Forearm Extensors',
-    ],
-  },
 ] as const;

src/ui/components/mobile/MobileMuscleList.tsx

@@ -42,29 +42,6 @@ export function MobileMuscleList({
     return new Map<string, VolumeStatItem>(stats.map((s) => [s.name, s]));
   }, [stats]);
 
-  // Calculate group summaries for header display
-  const groupSummaries = useMemo(() => {
-    const summaries = new Map<
-      string,
-      { totalVolume: number; totalGoal: number; percentage: number }
-    >();
-
-    for (const group of UI_MUSCLE_GROUPS) {
-      let totalVolume = 0;
-      let totalGoal = 0;
-
-      for (const muscle of group.muscles) {
-        const muscleStats = statsMap.get(muscle);
-        totalVolume += muscleStats?.volume ?? 0;
-        totalGoal += muscleStats?.goal ?? 0;
-      }
-
-      const percentage = totalGoal > 0 ? (totalVolume / totalGoal) * 100 : 0;
-      summaries.set(group.name, { totalVolume, totalGoal, percentage });
-    }
-
-    return summaries;
-  }, [statsMap]);
 
   // Start with first group expanded (mobile-optimized: less initial scrolling)
   const [expandedGroups, setExpandedGroups] = useState<Set<string>>(() => {
@@ -105,9 +82,6 @@ export function MobileMuscleList({
     <div className="space-y-2">
       {UI_MUSCLE_GROUPS.map((group) => {
         const isExpanded = expandedGroups.has(group.name);
-        const summary = groupSummaries.get(group.name);
-        const groupPercentage = summary?.percentage ?? 0;
-        const groupVolume = summary?.totalVolume ?? 0;
 
         return (
           <div
@@ -138,36 +112,31 @@ export function MobileMuscleList({
 
               {/* Group name */}
               <span className="font-medium text-white">{group.name}</span>
-
-              {/* Group summary - total sets with color indicating progress */}
-              <div className="ml-auto flex items-center gap-2">
-                <span
-                  className="font-mono text-sm"
-                  style={{ color: getVolumeColor(groupPercentage) }}
-                >
-                  {formatVolume(groupVolume)}
-                </span>
-                <span className="text-primary-400 text-xs">sets</span>
-              </div>
             </button>
 
             {/* Group content - conditionally rendered */}
             {isExpanded && (
-              <div className="bg-primary-900 p-3 space-y-1">
+              <div className="bg-primary-900 p-3 space-y-3">
                 {group.muscles.map((muscle) => {
                   const muscleStats = statsMap.get(muscle);
                   const volume = muscleStats?.volume ?? 0;
+                  const goal = muscleStats?.goal ?? 0;
                   const percentage = muscleStats?.percentage ?? 0;
 
                   return (
-                    <div key={muscle} className="flex items-center gap-3 py-2">
-                      {/* Muscle name - flex-1 for overflow handling */}
-                      <span className="flex-1 text-sm text-primary-200 truncate">
-                        {muscle}
-                      </span>
-
-                      {/* Progress bar container - fixed width for consistency */}
-                      <div className="w-24 h-2 overflow-hidden rounded-full bg-primary-800">
+                    <div key={muscle} className="space-y-1">
+                      {/* Line 1: Muscle name (left) + volume/goal ratio (right) */}
+                      <div className="flex items-center justify-between">
+                        <span className="text-sm text-primary-200">
+                          {muscle}
+                        </span>
+                        <span className="text-xs text-primary-400 font-mono">
+                          {formatVolume(volume)}/{formatVolume(goal)}
+                        </span>
+                      </div>
+
+                      {/* Line 2: Progress bar - 4px tall (h-1), full width */}
+                      <div className="w-full h-1 overflow-hidden rounded-full bg-primary-800">
                         <div
                           className="h-full rounded-full transition-all duration-300"
                           style={{
@@ -176,11 +145,6 @@ export function MobileMuscleList({
                           }}
                         />
                       </div>
-
-                      {/* Numeric value - secondary emphasis (LIST-04) */}
-                      <span className="w-12 text-right text-xs text-primary-400 font-mono">
-                        {formatVolume(volume)}
-                      </span>
                     </div>
                   );
                 })}