add CLI enhancements and scheduled cleanup

CLI commands:
- list: show user's pastes with pagination
- search: filter by type (glob), after/before timestamps
- update: modify content, password, or extend expiry
- export: save pastes to directory with optional decryption

API changes:
- PUT /<id>: update paste content and metadata
- GET /pastes: add type, after, before query params

Scheduled tasks:
- Thread-safe cleanup with per-task intervals
- Activate cleanup_expired_hashes (15min)
- Activate cleanup_rate_limits (5min)

Tests: 205 passing

tests/conftest.py

@@ -2,14 +2,37 @@
 
 import pytest
 
+import app.database as db_module
 from app import create_app
+from app.api.routes import reset_rate_limits
+
+
+def _clear_database():
+    """Clear all data from database tables for test isolation."""
+    if db_module._memory_db_holder is not None:
+        db_module._memory_db_holder.execute("DELETE FROM pastes")
+        db_module._memory_db_holder.execute("DELETE FROM content_hashes")
+        db_module._memory_db_holder.execute("DELETE FROM issued_certificates")
+        db_module._memory_db_holder.execute("DELETE FROM certificate_authority")
+        db_module._memory_db_holder.commit()
 
 
 @pytest.fixture
 def app():
     """Create application for testing."""
-    app = create_app("testing")
-    yield app
+    # Reset global state for test isolation
+    reset_rate_limits()
+    _clear_database()
+
+    test_app = create_app("testing")
+
+    # Clear database again after app init (in case init added anything)
+    _clear_database()
+
+    yield test_app
+
+    # Cleanup after test
+    reset_rate_limits()
 
 
 @pytest.fixture