feat(adr-117/p4): pure-Python WS/MQTT client layer

New sub-package `wifi_densepose.client` (no PyO3, no Rust deps):

- ws.SensingClient — asyncio websockets>=12 wrapper for the Rust
  sensing-server /ws/sensing endpoint. Yields typed dataclasses
  (ConnectionEstablishedMessage, EdgeVitalsMessage, PoseDataMessage)
  with raw-payload fallback for forward-compat with unknown types.
  Malformed frames log+drop without breaking the stream.

- mqtt.RuViewMqttClient — paho-mqtt v2 wrapper using the explicit
  CallbackAPIVersion.VERSION2 API. Per-instance unique client_id by
  default (rumqttc memory lesson). MQTT v5-spec-correct topic
  wildcard matcher: + as whole-level wildcard, # matches the prefix
  itself plus all sub-levels. Auto-resubscribes on reconnect.
  Handler exceptions are caught and logged so a misbehaving callback
  can't crash the network loop.

- primitives.SemanticPrimitiveListener — typed router for the 10
  HA-MIND fused inference outputs from ADR-115 §3.12
  (SomeoneSleeping, PossibleDistress, RoomActive, ElderlyInactivity-
  Anomaly, MeetingInProgress, BathroomOccupied, FallRiskElevated,
  BedExit, NoMovementSafety, MultiRoomTransition). Decodes both
  JSON payloads with confidence+explanation AND plain HA state
  strings ("ON"/"OFF"/numeric). Pluggable into RuViewMqttClient.

- ha.HABlueprintHelper — read-only parser for the
  homeassistant/<kind>/wifi_densepose_<node>/<id>/config payload
  family. Aggregator queries: entities_for_node, by_device_class,
  nodes. Useful for blueprint authors + dashboard introspection.

Test coverage (63 new tests, 156 total in Python suite):
- test_client_ha — 18 tests (topic+payload parsing, aggregator)
- test_client_primitives — 13 tests (enum coverage, listener routing)
- test_client_mqtt — 17 tests (matcher parametrize, dispatch path,
  on_connect, exception isolation) — no broker needed
- test_client_ws — 6 tests including end-to-end against an in-process
  websockets.serve() fixture exercising all 4 message types plus a
  malformed-frame survival check

Post-bridge wheel size: 238 KB (well under ADR §5.4 5 MB budget).

Refs: docs/adr/ADR-117-pip-wifi-densepose-modernization.md §5.6
Refs: docs/adr/ADR-115-home-assistant-integration.md §3.12
Refs: #785

Co-Authored-By: claude-flow <ruv@ruv.net>

python/wifi_densepose/client/__init__.py

@@ -0,0 +1,93 @@
+"""ADR-117 P4 — Pure-Python client layer.
+
+This sub-package is the **client-facing** half of `wifi-densepose`:
+end users who only want to *consume* live RuView telemetry (rather than
+running DSP locally) get a tight, opt-in client extra:
+
+```
+pip install "wifi-densepose[client]"
+```
+
+The runtime install footprint stays small for users who only need the
+compiled PyO3 surface: `websockets` and `paho-mqtt` are declared as the
+`[client]` extra in `pyproject.toml` and are NOT pulled in by the
+default install.
+
+## Modules
+
+- `ws` — `SensingClient`: asyncio WebSocket client for the
+  sensing-server `/ws/sensing` endpoint (ADR-115 §1)
+- `mqtt` — `RuViewMqttClient`: paho-mqtt v2 wrapper for
+  `ruview/<node>/raw/+` + `homeassistant/+/wifi_densepose_<node>/+/+`
+  topics (ADR-115 §3)
+- `primitives` — `SemanticPrimitiveListener`: typed view over the
+  10 HA-MIND semantic primitives (ADR-115 §3.12)
+- `ha` — `HABlueprintHelper`: parses MQTT-discovery payloads, helps
+  users introspect what entities a node is publishing
+
+No PyO3 here — this module is pure Python so it loads without the
+compiled extension (useful for users who only want the client surface
+and not the DSP pipeline).
+"""
+
+from __future__ import annotations
+
+# Re-export the user-facing types. Import errors are deferred to the
+# moment the user actually instantiates one of these classes — that way
+# `from wifi_densepose.client import HABlueprintHelper` still works
+# even if the user hasn't installed `[client]` extras yet (HABlueprint
+# is pure stdlib).
+from wifi_densepose.client.ha import (
+    HaDiscoveryPayload,
+    HaEntity,
+    HABlueprintHelper,
+)
+from wifi_densepose.client.primitives import (
+    SemanticPrimitive,
+    SemanticPrimitiveEvent,
+    SemanticPrimitiveListener,
+)
+
+
+__all__ = [
+    # ws — re-exported lazily; see module docstring
+    "SensingClient",
+    "SensingMessage",
+    "EdgeVitalsMessage",
+    "PoseDataMessage",
+    "ConnectionEstablishedMessage",
+    # mqtt — re-exported lazily; see module docstring
+    "RuViewMqttClient",
+    # ha — pure stdlib
+    "HaDiscoveryPayload",
+    "HaEntity",
+    "HABlueprintHelper",
+    # primitives — pure stdlib
+    "SemanticPrimitive",
+    "SemanticPrimitiveEvent",
+    "SemanticPrimitiveListener",
+]
+
+
+def __getattr__(name: str):
+    """Lazy re-exports for the modules that pull in optional extras.
+
+    `SensingClient` needs `websockets`; `RuViewMqttClient` needs
+    `paho-mqtt`. Importing those at package init would make
+    `wifi_densepose.client` unusable without the extras installed
+    — defeating the point of an *optional* extra. We defer the import
+    until the attribute is actually looked up.
+    """
+    if name in {
+        "SensingClient",
+        "SensingMessage",
+        "EdgeVitalsMessage",
+        "PoseDataMessage",
+        "ConnectionEstablishedMessage",
+    }:
+        from wifi_densepose.client import ws as _ws
+        return getattr(_ws, name)
+    if name == "RuViewMqttClient":
+        from wifi_densepose.client.mqtt import RuViewMqttClient as _R
+        return _R
+    raise AttributeError(f"module 'wifi_densepose.client' has no attribute {name!r}")