Add main CLI entry point and full test suite

- bigbrother.py: Click CLI with start/stop/status/activate/deactivate/
  kill/config/selftest/modules commands plus Rich interactive menu.
  Module discovery scans modules/stealth/ for BaseModule subclasses.
  Supports --daemon mode with PID file and --passive-only flag.
- tests/conftest.py: Shared fixtures (tmp_dir, mock_config, mock_bus,
  mock_state, hardware_tier_override, project_root)
- tests/test_bus.py: 6 tests for EventBus pub/sub, filtering, wildcards
- tests/test_engine.py: 5 tests for Engine lifecycle, deps, tier, phase
- tests/test_crypto.py: 5 tests for AES-256-GCM, file encryption, KDF
- tests/test_resource.py: 7 tests for hardware detection, memory, disk
- tests/test_tool_manager.py: 6 tests for subprocess management
- tests/test_stealth_modules.py: 4 parametrized test classes covering
  all 12 stealth modules (import, inheritance, attributes, instantiation)

tests/conftest.py

@@ -0,0 +1,117 @@
+"""Shared pytest fixtures for BigBrother tests."""
+
+import os
+import sys
+import tempfile
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+# ---------------------------------------------------------------------------
+# Ensure project root is on sys.path
+# ---------------------------------------------------------------------------
+
+PROJECT_ROOT = str(Path(__file__).resolve().parent.parent)
+if PROJECT_ROOT not in sys.path:
+    sys.path.insert(0, PROJECT_ROOT)
+
+
+@pytest.fixture
+def project_root():
+    """Return the project root directory and ensure it is on sys.path."""
+    return PROJECT_ROOT
+
+
+@pytest.fixture
+def tmp_dir(tmp_path):
+    """Provide a temporary directory for test artifacts."""
+    return str(tmp_path)
+
+
+@pytest.fixture
+def mock_config():
+    """Return a valid BigBrother config dict (no YAML file needed)."""
+    return {
+        "device": {
+            "platform": "generic",
+            "hostname": "test-device",
+            "install_path": "/tmp/bb-test",
+        },
+        "network": {
+            "primary_interface": "eth0",
+            "scope_enforcement": False,
+        },
+        "connectivity": {
+            "primary": "wireguard",
+        },
+        "security": {
+            "encryption": "aes-256-gcm",
+            "encryption_key_derive": "argon2id",
+            "kill_switch_enabled": True,
+        },
+        "capture": {
+            "interface": "eth0",
+            "snap_length": 65535,
+            "pcap_rotation_hours": 1,
+            "pcap_compression": "zstd",
+            "pcap_compression_level": 19,
+        },
+        "stealth": {
+            "mac_profile": "auto",
+            "process_disguise": True,
+            "log_suppression": True,
+        },
+        "engagement_phase": {
+            "mode": "passive_only",
+            "passive_days": 7,
+        },
+        "bettercap": {
+            "binary": "/usr/local/bin/bettercap",
+            "api_address": "127.0.0.1",
+            "api_port": 8083,
+        },
+        "storage_path": "/tmp/bb-test/storage",
+    }
+
+
+@pytest.fixture
+def mock_bus():
+    """Return a started EventBus instance. Stopped after test."""
+    from core.bus import EventBus
+
+    bus = EventBus()
+    bus.start()
+    yield bus
+    bus.stop()
+
+
+@pytest.fixture
+def mock_state(tmp_path):
+    """Return a StateManager backed by a temp SQLite database. Stopped after test."""
+    from core.state import StateManager
+
+    db_path = str(tmp_path / "test_state.db")
+    state = StateManager(db_path=db_path)
+    state.start()
+    yield state
+    state.stop()
+
+
+@pytest.fixture
+def hardware_tier_override():
+    """Context manager fixture to patch detect_hardware_tier to return a specific tier.
+
+    Usage:
+        def test_foo(hardware_tier_override):
+            with hardware_tier_override("pi_zero"):
+                ...
+    """
+    from contextlib import contextmanager
+
+    @contextmanager
+    def _override(tier: str):
+        with patch("core.engine.detect_hardware_tier", return_value=tier):
+            yield
+
+    return _override