4.1 routing quality + 4.4 persona prompt

- VoiceConfig: add QueryMinScore (default 0.55) + Persona config fields
- voice.go: remove queryMinScore const, wire from cfg.Voice.QueryMinScore
  as reactiveHandler field
- llmphraser.go: add Persona to Config, prepend to system prompts in
  chat and query paths (systemPrompt/querySystemPrompt methods)
- main.go: pass personaFromCfg into both phraser config blocks
- Makefile: add download-embedder target (Xenova/paraphrase-multilingual-
  MiniLM-L12-v2, ~90MB ONNX)
- AGENTS.md: document embedder model download + libonnxruntime setup
- server.go: fix pre-existing wg.Add vs wg.Wait data race using accept
  mutex. make test green, zero races across all 29 packages.

Makefile

@@ -8,7 +8,7 @@ PIPER_BIN     := $(shell pwd)/deps/piper/piper
 PIPER_MODEL   := $(shell pwd)/models/tts/ru_RU-irina-medium.onnx
 PIPER_ESPEAK  := $(shell pwd)/deps/piper/espeak-ng-data
 
-.PHONY: all build build-stt build-tts build-daemon build-client build-web build-poll build-caldav clean test run-stt run-tts run-web
+.PHONY: all build build-stt build-tts build-daemon build-client build-web build-poll build-caldav clean test run-stt run-tts run-web download-embedder
 
 all: build
 
@@ -71,5 +71,30 @@ deps-piper:
 		-o /tmp/piper.tar.gz
 	tar -xzf /tmp/piper.tar.gz -C deps/
 
+EMBEDDER_DIR := $(shell pwd)/models/embedder
+EMBEDDER_MODEL_URL := https://huggingface.co/Xenova/paraphrase-multilingual-MiniLM-L12-v2/resolve/main/onnx/model_quantized.onnx
+EMBEDDER_TOKENIZER_URL := https://huggingface.co/Xenova/paraphrase-multilingual-MiniLM-L12-v2/resolve/main/tokenizer.json
+
+download-embedder:
+	mkdir -p $(EMBEDDER_DIR)
+	curl -sL "$(EMBEDDER_MODEL_URL)" -o "$(EMBEDDER_DIR)/model_quantized.onnx"
+	curl -sL "$(EMBEDDER_TOKENIZER_URL)" -o "$(EMBEDDER_DIR)/tokenizer.json"
+	@echo ""
+	@echo "embedder model downloaded to $(EMBEDDER_DIR)/"
+	@echo "To use it, add to mavend.json:"
+	@echo '  "voice": {'
+	@echo '    ...'
+	@echo '    "embedder": {'
+	@echo '      "model_path": "$(EMBEDDER_DIR)/model_quantized.onnx",'
+	@echo '      "tokenizer_path": "$(EMBEDDER_DIR)/tokenizer.json",'
+	@echo '      "lib_path": "/path/to/libonnxruntime.so"'
+	@echo '    }'
+	@echo '  }'
+	@echo ""
+	@echo "Install libonnxruntime.so from: https://github.com/microsoft/onnxruntime/releases"
+	@echo "e.g. on x86_64 Linux:"
+	@echo '  curl -sL "https://github.com/microsoft/onnxruntime/releases/download/v1.15.1/onnxruntime-linux-x64-1.15.1.tgz" | tar xz'
+	@echo '  sudo cp onnxruntime-linux-x64-1.15.1/lib/libonnxruntime.so* /usr/local/lib/'
+
 clean:
 	rm -f mavend mavenclient mavsttd mavttsd mavweb mavpoll mavcaldav