feat(web): implement responsive modal pattern for mobile-friendly NPC chat

- Add hybrid modal/page navigation based on screen size (1024px breakpoint)
- Desktop (>1024px): Uses modal overlays for quick interactions
- Mobile (≤1024px): Navigates to dedicated full pages for better UX
- Extract shared NPC chat content into reusable partial template
- Add responsive navigation JavaScript (responsive-modals.js)
- Create dedicated NPC chat page route with back button navigation
- Add mobile-optimized CSS with sticky header and chat input
- Fix HTMX indicator errors by using htmx-indicator class pattern
- Document responsive modal pattern for future features

Addresses mobile UX issues: cramped space, nested scrolling, keyboard conflicts,
and lack of native back button support in modals.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

public_web/app/views/game_views.py

@@ -690,10 +690,66 @@ def do_travel(session_id: str):
         return f'<div class="error">Travel failed: {e}</div>', 500
 
 
+@game_bp.route('/session/<session_id>/npc/<npc_id>')
+@require_auth
+def npc_chat_page(session_id: str, npc_id: str):
+    """
+    Dedicated NPC chat page (mobile-friendly full page view).
+    Used on mobile devices for better UX.
+    """
+    client = get_api_client()
+
+    try:
+        # Get session to find character
+        session_response = client.get(f'/api/v1/sessions/{session_id}')
+        session_data = session_response.get('result', {})
+        character_id = session_data.get('character_id')
+
+        # Get NPC details with relationship info
+        npc_response = client.get(f'/api/v1/npcs/{npc_id}?character_id={character_id}')
+        npc_data = npc_response.get('result', {})
+
+        npc = {
+            'npc_id': npc_data.get('npc_id'),
+            'name': npc_data.get('name'),
+            'role': npc_data.get('role'),
+            'appearance': npc_data.get('appearance', {}).get('brief', ''),
+            'tags': npc_data.get('tags', []),
+            'image_url': npc_data.get('image_url')
+        }
+
+        # Get relationship info
+        interaction_summary = npc_data.get('interaction_summary', {})
+        relationship_level = interaction_summary.get('relationship_level', 50)
+        interaction_count = interaction_summary.get('interaction_count', 0)
+
+        # Conversation history would come from character's npc_interactions
+        # For now, we'll leave it empty - the API returns it in dialogue responses
+        conversation_history = []
+
+        return render_template(
+            'game/npc_chat_page.html',
+            session_id=session_id,
+            npc=npc,
+            conversation_history=conversation_history,
+            relationship_level=relationship_level,
+            interaction_count=interaction_count
+        )
+
+    except APINotFoundError:
+        return render_template('errors/404.html', message="NPC not found"), 404
+    except APIError as e:
+        logger.error("failed_to_load_npc_chat_page", session_id=session_id, npc_id=npc_id, error=str(e))
+        return render_template('errors/500.html', message=f"Failed to load NPC: {e}"), 500
+
+
 @game_bp.route('/session/<session_id>/npc/<npc_id>/chat')
 @require_auth
 def npc_chat_modal(session_id: str, npc_id: str):
-    """Get NPC chat modal with conversation history."""
+    """
+    Get NPC chat modal with conversation history.
+    Used on desktop for modal overlay experience.
+    """
     client = get_api_client()
 
     try: