fix: resolve NPC chat database persistence and modal targeting

Fixed two critical bugs in NPC chat functionality:

  1. Database Persistence - Metadata serialization bug
     - Empty dict {} was falsy, preventing JSON conversion
     - Changed to unconditional serialization in ChatMessageService
     - Messages now successfully save to chat_messages collection

  2. Modal Targeting - HTMX targeting lost during polling
     - poll_job() wasn't preserving hx-target/hx-swap parameters
     - Pass targeting params through query string in polling cycle
     - Responses now correctly load in modal instead of main panel

  Files modified:
  - api/app/services/chat_message_service.py
  - public_web/templates/game/partials/job_polling.html
  - public_web/app/views/game_views.py

public_web/app/views/game_views.py

@@ -506,6 +506,10 @@ def poll_job(session_id: str, job_id: str):
     """Poll job status - returns updated partial."""
     client = get_api_client()
 
+    # Get hx_target and hx_swap from query params (passed through from original request)
+    hx_target = request.args.get('_hx_target')
+    hx_swap = request.args.get('_hx_swap')
+
     try:
         response = client.get(f'/api/v1/jobs/{job_id}/status')
         result = response.get('result', {})
@@ -540,11 +544,14 @@ def poll_job(session_id: str, job_id: str):
 
         else:
             # Still processing - return polling partial to continue
+            # Pass through hx_target and hx_swap to maintain targeting
             return render_template(
                 'game/partials/job_polling.html',
                 session_id=session_id,
                 job_id=job_id,
-                status=status
+                status=status,
+                hx_target=hx_target,
+                hx_swap=hx_swap
             )
 
     except APIError as e:
@@ -767,12 +774,15 @@ def talk_to_npc(session_id: str, npc_id: str):
         job_id = result.get('job_id')
         if job_id:
             # Return job polling partial for the chat area
+            # Use hx-target="this" and hx-swap="outerHTML" to replace loading div with response in-place
             return render_template(
                 'game/partials/job_polling.html',
                 job_id=job_id,
                 session_id=session_id,
                 status='queued',
-                is_npc_dialogue=True
+                is_npc_dialogue=True,
+                hx_target='this',       # Target the loading div itself
+                hx_swap='outerHTML'     # Replace entire loading div with response
             )
 
         # Immediate response (if AI is sync or cached)

public_web/templates/game/partials/job_polling.html

@@ -10,10 +10,10 @@ Shows loading state while waiting for AI response, auto-polls for completion
 {% endif %}
 
 <div class="loading-state"
-     hx-get="{{ url_for('game.poll_job', session_id=session_id, job_id=job_id) }}"
+     hx-get="{{ url_for('game.poll_job', session_id=session_id, job_id=job_id, _hx_target=hx_target, _hx_swap=hx_swap) }}"
      hx-trigger="load delay:1s"
-     hx-swap="innerHTML"
-     hx-target="#narrative-content">
+     hx-swap="{{ hx_swap|default('innerHTML') }}"
+     hx-target="{{ hx_target|default('#narrative-content') }}">
     <div class="loading-spinner-large"></div>
     <p class="loading-text">
         {% if status == 'queued' %}