feat(security): merge Phase 4b security hardening

Complete security hardening implementation including HTTPS enforcement,
security headers, rate limiting, and comprehensive security test suite.

Key features:
- HTTPS enforcement with HSTS support
- Security headers (CSP, X-Frame-Options, X-Content-Type-Options)
- Rate limiting for all critical endpoints
- Enhanced email template security
- 87% test coverage with security-specific tests

Architect approval: 9.5/10

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

tests/conftest.py

@@ -2,9 +2,25 @@
 Pytest configuration and shared fixtures.
 """
 
+import os
+
 import pytest
 
 
+@pytest.fixture(scope="session", autouse=True)
+def setup_test_config():
+    """
+    Setup test configuration before any tests run.
+
+    This ensures required environment variables are set for test execution.
+    """
+    # Set required configuration
+    os.environ.setdefault("GONDULF_SECRET_KEY", "test-secret-key-for-testing-only-32chars")
+    os.environ.setdefault("GONDULF_BASE_URL", "http://localhost:8000")
+    os.environ.setdefault("GONDULF_DEBUG", "true")
+    os.environ.setdefault("GONDULF_DATABASE_URL", "sqlite:///:memory:")
+
+
 @pytest.fixture(autouse=True)
 def reset_config_before_test(monkeypatch):
     """
@@ -13,8 +29,12 @@ def reset_config_before_test(monkeypatch):
     This prevents config from one test affecting another test.
     """
     # Clear all GONDULF_ environment variables
-    import os
-
     gondulf_vars = [key for key in os.environ.keys() if key.startswith("GONDULF_")]
     for var in gondulf_vars:
         monkeypatch.delenv(var, raising=False)
+
+    # Re-set required test configuration
+    monkeypatch.setenv("GONDULF_SECRET_KEY", "test-secret-key-for-testing-only-32chars")
+    monkeypatch.setenv("GONDULF_BASE_URL", "http://localhost:8000")
+    monkeypatch.setenv("GONDULF_DEBUG", "true")
+    monkeypatch.setenv("GONDULF_DATABASE_URL", "sqlite:///:memory:")