feat(deploy): add brain/app roles for GPU-split deployment

Run the GPU-heavy compute (Whisper STT, Ollama LLM, TTS) on a dedicated
brain host and the bot + browser on a separate no-GPU app host, talking
over the LAN.

- supervisord: new `brain` role (bridge only) and `app` role (bot +
  desktop/Chrome, no local bridge); `full`/`browser`/`bot` unchanged.
- compose: make BRIDGE_URL overridable (was hardcoded to loopback, which
  prevented the bot from reaching a remote bridge).
- docs: DEPLOY.md "GPU split" layout with per-host .env blocks; document
  the new roles in run-if-role.sh and .env.example.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.env.example

@@ -29,7 +29,9 @@ BRIDGE_PORT=8765
 JARVIS_BRAIN_ENABLED=1
 JARVIS_TTS_ENABLED=1
 # faster-whisper device/compute. GPU by default (RTX 5050 / sm_120, verified).
-# Falls back to CPU automatically if no GPU is passed to the container.
+# On a NO-GPU host (e.g. an app host that offloads the LLM to a separate GPU box)
+# set WHISPER_DEVICE=cpu AND WHISPER_COMPUTE_TYPE=int8 — float16 is GPU-only, so
+# CPU needs int8 (STT is slower on CPU).
 WHISPER_DEVICE=cuda
 WHISPER_COMPUTE_TYPE=float16
 # Optional explicit Piper voice model (.onnx). If empty, the jarvis default is used.
@@ -203,6 +205,10 @@ VOICE_SILENCE_MS=800
 #   full     (default) everything in one container
 #   browser  ONLY the desktop + Chrome + control-server (driven over the LAN)
 #   bot      ONLY the bot + bridge + TTS (drives a REMOTE browser)
+#   brain    ONLY the bridge (STT + reply + TTS) on a GPU host — no bot/desktop.
+#            The app host reaches it via BRIDGE_URL. See docs/DEPLOY.md "GPU split".
+#   app      the bot + desktop/Chrome, but NOT the local bridge: offloads
+#            STT/LLM/TTS to a remote brain host (set BRIDGE_URL=http://<brain>:8765).
 JARVIS_ROLE=full
 
 # --- GPU per OS: pick the matching compose override via COMPOSE_FILE ---