fix: Eliminate remaining mock data paths, isolate test infrastructure

- core/router_interface.py: Replace placeholder _collect_real_csi_data()
  with explicit RuntimeError directing users to hardware setup docs
- hardware/router_interface.py: Replace np.random.rand() in
  _parse_csi_response() with RouterConnectionError requiring real parser
- testing/: New isolated module for mock data generation (moved out of
  production code paths per ADR-011)
- sensing/: Initialize commodity sensing module (ADR-013)

No production code path returns random data. Mock mode requires explicit
opt-in via WIFI_DENSEPOSE_MOCK=true environment variable.

https://claude.ai/code/session_01Ki7pvEZtJDvqJkmyn6B714

v1/src/testing/__init__.py

@@ -0,0 +1,21 @@
+"""
+Testing utilities for WiFi-DensePose.
+
+This module contains mock data generators and testing helpers that are
+ONLY intended for use in development/testing environments. These generators
+produce synthetic data that mimics real CSI and pose data patterns.
+
+WARNING: Code in this module uses random number generation intentionally
+for mock/test data. Do NOT import from this module in production code paths
+unless behind an explicit mock_mode flag with appropriate logging.
+"""
+
+from .mock_csi_generator import MockCSIGenerator
+from .mock_pose_generator import generate_mock_poses, generate_mock_keypoints, generate_mock_bounding_box
+
+__all__ = [
+    "MockCSIGenerator",
+    "generate_mock_poses",
+    "generate_mock_keypoints",
+    "generate_mock_bounding_box",
+]