Simplify opening training: train on entire opening family instead of single variation

- Add family training mode where users select an opening family (e.g. "Italian Game")
  and can play any variation within that family
- Create variation tree data structure to efficiently track which variations
  match the current move sequence
- FamilySelector now navigates directly to /learning/openings/family/[familyName]
  instead of showing a second selector for individual variations
- OpeningTrainer displays matching variations, possible moves, and current line
- LLM tutor explains which variation is being played and mentions alternatives
- Remove the OpeningSelector step from the flow for a simpler UX

The new flow:
1. User selects an opening family (e.g. "Sicilian Defense")
2. Training starts immediately with all variations loaded
3. User can play any move that exists in any variation
4. The UI shows which variations are still possible
5. The AI tutor guides the user through the repertoire

src/components/Tutor.tsx

@@ -82,6 +82,14 @@ interface TutorProps {
         wikipediaSummary?: string;  // Optional Wikipedia context
         shouldTutorSpeak?: boolean;  // Guardrail: controls when tutor can send messages
         onTutorMessageSent?: () => void;  // Callback when tutor sends a message
+        // Family mode: training with multiple variations
+        isFamilyMode?: boolean;
+        variationInfo?: {
+            matchingVariations: number;
+            currentVariationNames: string[];
+            possibleMoves: string[];
+            isEndOfLine: boolean;
+        };
     };
 }
 
@@ -359,6 +367,8 @@ Acknowledge this new puzzle briefly (1 sentence) and encourage the student to fi
     const isInTheory = openingPracticeMode?.isInTheory ?? true;
     const currentFeedback = openingPracticeMode?.currentFeedback;
     const repertoireMovesLength = openingPracticeMode?.repertoireMoves?.length ?? 0;
+    const isFamilyMode = openingPracticeMode?.isFamilyMode ?? false;
+    const variationInfo = openingPracticeMode?.variationInfo;
 
     // Automatic commentary for opening practice mode
     useEffect(() => {
@@ -382,6 +392,14 @@ Acknowledge this new puzzle briefly (1 sentence) and encourage the student to fi
         if (userMoveKey && userMoveKey !== lastUserMoveRef.current) {
             lastUserMoveRef.current = userMoveKey;
 
+            // Build variation context for family mode
+            const variationContext = isFamilyMode && variationInfo ? `
+Variation info:
+- Matching variations: ${variationInfo.matchingVariations}
+- Current line(s): ${variationInfo.currentVariationNames.slice(0, 3).join(', ')}${variationInfo.currentVariationNames.length > 3 ? '...' : ''}
+- Possible next moves: ${variationInfo.possibleMoves.join(', ') || 'none (end of line)'}
+${variationInfo.isEndOfLine ? '- This is the end of this variation line' : ''}` : '';
+
             // Generate commentary about user's move
             const moveCommentary = `
 [SYSTEM TRIGGER: user_move_in_opening]
@@ -391,13 +409,25 @@ Move category: ${currentFeedback?.category || 'unknown'}
 Position status: ${isInTheory ? 'In theory' : 'Deviated from repertoire'}
 ${currentFeedback?.evaluationChange !== undefined ? `Evaluation change: ${currentFeedback.evaluationChange.toFixed(2)}` : ''}
 ${currentFeedback?.theoreticalAlternatives && currentFeedback.theoreticalAlternatives.length > 0 ? `Theory suggested: ${currentFeedback.theoreticalAlternatives.join(', ')}` : ''}
+${variationContext}
 
 INSTRUCTIONS:
 ${isInTheory
-    ? `- The student is following the repertoire correctly - praise them briefly
+    ? isFamilyMode
+        ? `- The student is playing a valid move in the ${openingName} family
+- Tell them which specific variation(s) they're now in (if narrowed down)
+- Explain the key idea behind this move (1-2 sentences)
+- If there are multiple possible moves at this position, you can briefly mention alternatives
+- If you're about to make the next move, explain what it accomplishes`
+        : `- The student is following the repertoire correctly - praise them briefly
 - Explain the key idea behind this move (1-2 sentences)
 - If you're about to make the next move, you can mention it naturally`
-    : `- The student deviated from theory
+    : isFamilyMode
+        ? `- The student played a move not in any known variation of ${openingName}
+- Gently mention which moves would have been in theory (${currentFeedback?.theoreticalAlternatives?.join(' or ') || 'the main lines'})
+- Explain why those moves are preferred in the ${openingName}
+- Encourage them to explore or try a different move`
+        : `- The student deviated from theory
 - Gently point out what the repertoire move was
 - Explain why the repertoire move is preferred
 - Ask if they want to try again or continue exploring`}
@@ -469,7 +499,9 @@ Remember: You are both the opponent AND the tutor. Explain your move as if you'r
         language,
         openingName,
         currentFeedback,
-        repertoireMovesLength
+        repertoireMovesLength,
+        isFamilyMode,
+        variationInfo
     ]);
 
     // Scroll chat container to bottom (not the whole page)