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/API_TESTING.md

@@ -1447,6 +1447,166 @@ curl http://localhost:5000/api/v1/origins
 
 ---
 
+## Session Endpoints
+
+### 1. Create Session
+
+**Endpoint:** `POST /api/v1/sessions`
+
+**Description:** Create a new game session for a character. Subject to tier-based limits (Free: 1, Basic: 2, Premium: 3, Elite: 5).
+
+**Request:**
+
+```bash
+# httpie
+http --session=user1 POST localhost:5000/api/v1/sessions \
+  character_id="char_123"
+
+# curl
+curl -X POST http://localhost:5000/api/v1/sessions \
+  -H "Content-Type: application/json" \
+  -b cookies.txt \
+  -d '{
+    "character_id": "char_123"
+  }'
+```
+
+**Success Response (201 Created):**
+
+```json
+{
+  "app": "Code of Conquest",
+  "version": "0.1.0",
+  "status": 201,
+  "timestamp": "2025-11-26T10:30:00Z",
+  "result": {
+    "session_id": "sess_789",
+    "character_id": "char_123",
+    "turn_number": 0,
+    "game_state": {
+      "current_location": "crossville_village",
+      "location_type": "town",
+      "active_quests": []
+    }
+  }
+}
+```
+
+**Error Response (409 Conflict - Session Limit Exceeded):**
+
+```json
+{
+  "app": "Code of Conquest",
+  "version": "0.1.0",
+  "status": 409,
+  "timestamp": "2025-11-26T10:30:00Z",
+  "error": {
+    "code": "SESSION_LIMIT_EXCEEDED",
+    "message": "Maximum active sessions reached for free tier (1/1). Please delete an existing session to start a new one."
+  }
+}
+```
+
+---
+
+### 2. List Sessions
+
+**Endpoint:** `GET /api/v1/sessions`
+
+**Description:** Get all active sessions for the authenticated user.
+
+**Request:**
+
+```bash
+# httpie
+http --session=user1 GET localhost:5000/api/v1/sessions
+
+# curl
+curl http://localhost:5000/api/v1/sessions -b cookies.txt
+```
+
+**Success Response (200 OK):**
+
+```json
+{
+  "app": "Code of Conquest",
+  "version": "0.1.0",
+  "status": 200,
+  "timestamp": "2025-11-26T10:30:00Z",
+  "result": [
+    {
+      "session_id": "sess_789",
+      "character_id": "char_123",
+      "turn_number": 5,
+      "status": "active",
+      "created_at": "2025-11-26T10:00:00Z",
+      "last_activity": "2025-11-26T10:25:00Z",
+      "game_state": {
+        "current_location": "crossville_village",
+        "location_type": "town"
+      }
+    }
+  ]
+}
+```
+
+---
+
+### 3. Delete Session
+
+**Endpoint:** `DELETE /api/v1/sessions/<session_id>`
+
+**Description:** Permanently delete a session and all associated chat messages. This frees up a session slot for your tier limit.
+
+**Request:**
+
+```bash
+# httpie
+http --session=user1 DELETE localhost:5000/api/v1/sessions/sess_789
+
+# curl
+curl -X DELETE http://localhost:5000/api/v1/sessions/sess_789 \
+  -b cookies.txt
+```
+
+**Success Response (200 OK):**
+
+```json
+{
+  "app": "Code of Conquest",
+  "version": "0.1.0",
+  "status": 200,
+  "timestamp": "2025-11-26T10:30:00Z",
+  "result": {
+    "message": "Session deleted successfully",
+    "session_id": "sess_789"
+  }
+}
+```
+
+**Error Response (404 Not Found):**
+
+```json
+{
+  "app": "Code of Conquest",
+  "version": "0.1.0",
+  "status": 404,
+  "timestamp": "2025-11-26T10:30:00Z",
+  "error": {
+    "code": "NOT_FOUND",
+    "message": "Session not found"
+  }
+}
+```
+
+**Note:** Deleting a session:
+- Permanently removes the session from the database
+- Deletes all chat messages associated with the session
+- Cannot be undone
+- Frees up a session slot for your tier limit
+
+---
+
 ## Testing Workflows
 
 ### Complete Registration Flow