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/sensing/__init__.py

@@ -0,0 +1,56 @@
+"""
+Commodity WiFi Sensing Module (ADR-013)
+=======================================
+
+RSSI-based presence and motion detection using standard Linux WiFi metrics.
+This module provides real signal processing from commodity WiFi hardware,
+extracting presence and motion features from RSSI time series.
+
+Components:
+    - rssi_collector: Data collection from Linux WiFi interfaces
+    - feature_extractor: Time-domain and frequency-domain feature extraction
+    - classifier: Presence and motion classification from features
+    - backend: Common sensing backend interface
+
+Capabilities:
+    - PRESENCE: Detect whether a person is present in the sensing area
+    - MOTION: Classify motion level (absent / still / active)
+
+Note: This module uses RSSI only. For higher-fidelity sensing (respiration,
+pose estimation), CSI-capable hardware and the full DensePose pipeline
+are required.
+"""
+
+from v1.src.sensing.rssi_collector import (
+    LinuxWifiCollector,
+    SimulatedCollector,
+    WifiSample,
+)
+from v1.src.sensing.feature_extractor import (
+    RssiFeatureExtractor,
+    RssiFeatures,
+)
+from v1.src.sensing.classifier import (
+    PresenceClassifier,
+    SensingResult,
+    MotionLevel,
+)
+from v1.src.sensing.backend import (
+    SensingBackend,
+    CommodityBackend,
+    Capability,
+)
+
+__all__ = [
+    "LinuxWifiCollector",
+    "SimulatedCollector",
+    "WifiSample",
+    "RssiFeatureExtractor",
+    "RssiFeatures",
+    "PresenceClassifier",
+    "SensingResult",
+    "MotionLevel",
+    "SensingBackend",
+    "CommodityBackend",
+    "Capability",
+]