feat(api,web): tier-based session limits and daily turn usage display

Backend Changes:
- Add tier-based max_sessions config (free: 1, basic: 2, premium: 3, elite: 5)
- Add DELETE /api/v1/sessions/{id} endpoint for hard session deletion
- Cascade delete chat messages when session is deleted
- Add GET /api/v1/usage endpoint for daily turn limit info
- Replace hardcoded TIER_LIMITS with config-based ai_calls_per_day
- Handle unlimited (-1) tier in rate limiter service

Frontend Changes:
- Add inline session delete buttons with HTMX on character list
- Add usage_display.html component showing remaining daily turns
- Display usage indicator on character list and game play pages
- Page refresh after session deletion to update UI state

Documentation:
- Update API_REFERENCE.md with new endpoints and tier limits
- Update API_TESTING.md with session endpoint examples
- Update SESSION_MANAGEMENT.md with tier-based limits

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

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

public_web/templates/game/partials/character_panel.html

@@ -10,6 +10,9 @@ Displays character stats, resource bars, and action buttons
             <span class="character-class">{{ character.class_name }}</span>
             <span class="character-level">Level {{ character.level }}</span>
         </div>
+        <div class="character-usage">
+            {% include 'components/usage_display.html' %}
+        </div>
     </div>
 
     {# Resource Bars #}