docs: add voice-assistant system map (Archify HTML + Mermaid source)

docs/voice-assistant.mmd

@@ -0,0 +1,29 @@
+flowchart LR
+    subgraph OnDevice["On-device"]
+        ESP32[ESP32-S3<br/>wake word · mic · LED]
+    end
+
+    subgraph Lab["Home lab (.13 · .30 · .35)"]
+        MQTT[(MQTT<br/>mosquitto :1883)]
+        WHISPER[Whisper STT<br/>faster-whisper]
+        AGENT[Jervis Agent<br/>FastAPI :8501]
+        HA[Home Assistant<br/>.30 :8123]
+        OMNI[OmniRoute<br/>LLM gateway :20129]
+        MOPIDY[Mopidy · Spotify<br/>music :6600]
+        APPRISE[Apprise<br/>notifications .35]
+        SNAP[Snapcast<br/>multi-room :1780]
+        PIPER[Piper TTS<br/>:10200]
+        SPEAKERS[House Speakers<br/>whole home]
+    end
+
+    ESP32 -->|audio stream| MQTT
+    MQTT -.->|speech frames| WHISPER
+    WHISPER -->|transcript| AGENT
+    AGENT -->|control · todo · timers| HA
+    AGENT -->|intent / Q&A| OMNI
+    AGENT -.->|play · pause · volume| MOPIDY
+    AGENT -.->|family messages| APPRISE
+    AGENT -->|reply text| SNAP
+    SNAP -.->|synthesize speech| PIPER
+    PIPER -->|speech wav| SNAP
+    SNAP -->|audio out| SPEAKERS