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>

api/docs/SESSION_MANAGEMENT.md

@@ -126,13 +126,21 @@ session = service.create_solo_session(
 
 **Validations:**
 - User must own the character
-- User cannot exceed 5 active sessions
+- User cannot exceed their tier's session limit
+
+**Session Limits by Tier:**
+| Tier | Max Sessions |
+|------|--------------|
+| FREE | 1 |
+| BASIC | 2 |
+| PREMIUM | 3 |
+| ELITE | 5 |
 
 **Returns:** `GameSession` instance
 
 **Raises:**
 - `CharacterNotFound` - Character doesn't exist or user doesn't own it
-- `SessionLimitExceeded` - User has 5+ active sessions
+- `SessionLimitExceeded` - User has reached their tier's session limit
 
 ### Retrieving Sessions
 
@@ -284,10 +292,18 @@ session = service.add_world_event(
 
 | Limit | Value | Notes |
 |-------|-------|-------|
-| Active sessions per user | 5 | End existing sessions to create new |
+| Active sessions per user | Tier-based (1-5) | See tier limits below |
 | Active quests per session | 2 | Complete or abandon to accept new |
 | Conversation history | Unlimited | Consider archiving for very long sessions |
 
+**Session Limits by Tier:**
+| Tier | Max Sessions |
+|------|--------------|
+| FREE | 1 |
+| BASIC | 2 |
+| PREMIUM | 3 |
+| ELITE | 5 |
+
 ---
 
 ## Database Schema
@@ -400,7 +416,7 @@ except SessionNotFound:
 try:
     service.create_solo_session(user_id, char_id)
 except SessionLimitExceeded:
-    # User has 5+ active sessions
+    # User has reached their tier's session limit
     pass
 
 try: