feat: implement 5 QA-driven security and quality proposals

Implemented proposals from comprehensive QA review:

1. extend-csrf-protection
   - Add POST to CSRF protected methods in frontend
   - Global CSRF middleware for all state-changing operations
   - Update tests with CSRF token fixtures

2. tighten-cors-websocket-security
   - Replace wildcard CORS with explicit method/header lists
   - Disable query parameter auth in production (code 4002)
   - Add per-user WebSocket connection limit (max 5, code 4005)

3. shorten-jwt-expiry
   - Reduce JWT expiry from 7 days to 60 minutes
   - Add refresh token support with 7-day expiry
   - Implement token rotation on refresh
   - Frontend auto-refresh when token near expiry (<5 min)

4. fix-frontend-quality
   - Add React.lazy() code splitting for all pages
   - Fix useCallback dependency arrays (Dashboard, Comments)
   - Add localStorage data validation in AuthContext
   - Complete i18n for AttachmentUpload component

5. enhance-backend-validation
   - Add SecurityAuditMiddleware for access denied logging
   - Add ErrorSanitizerMiddleware for production error messages
   - Protect /health/detailed with admin authentication
   - Add input length validation (comment 5000, desc 10000)

All 521 backend tests passing. Frontend builds successfully.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/tests/test_api_enhancements.py

@@ -173,7 +173,7 @@ class TestProjectTemplates:
         # Should return list of templates
         assert "templates" in data or isinstance(data, list)
 
-    def test_create_template(self, client, admin_token, db):
+    def test_create_template(self, client, auth_headers, db):
         """Test creating a new project template."""
         from app.models import Space
 
@@ -192,14 +192,14 @@ class TestProjectTemplates:
                     {"name": "Done", "color": "#00FF00"}
                 ]
             },
-            headers={"Authorization": f"Bearer {admin_token}"}
+            headers=auth_headers
         )
 
         assert response.status_code in [200, 201]
         data = response.json()
         assert data.get("name") == "Test Template"
 
-    def test_create_project_from_template(self, client, admin_token, db):
+    def test_create_project_from_template(self, client, auth_headers, db):
         """Test creating a project from a template."""
         from app.models import Space, ProjectTemplate
 
@@ -228,14 +228,14 @@ class TestProjectTemplates:
                 "description": "Created from template",
                 "template_id": "test-template-id"
             },
-            headers={"Authorization": f"Bearer {admin_token}"}
+            headers=auth_headers
         )
 
         assert response.status_code in [200, 201]
         data = response.json()
         assert data.get("name") == "Project from Template"
 
-    def test_delete_template(self, client, admin_token, db):
+    def test_delete_template(self, client, auth_headers, db):
         """Test deleting a project template."""
         from app.models import ProjectTemplate
 
@@ -251,7 +251,7 @@ class TestProjectTemplates:
 
         response = client.delete(
             "/api/templates/delete-template-id",
-            headers={"Authorization": f"Bearer {admin_token}"}
+            headers=auth_headers
         )
 
         assert response.status_code in [200, 204]