feat: rewrite chat-handler in Go

Replace Python chat handler with Go for smaller container images.
Uses handler-base Go module for NATS, health, telemetry, and service clients.

- RAG pipeline: embed → Milvus → rerank → LLM
- Streaming response chunks
- Optional TTS synthesis
- Custom response_subject support for companions-frontend

main_test.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"os"
+	"testing"
+)
+
+func TestStrVal(t *testing.T) {
+	m := map[string]any{"key": "value", "num": 42}
+	if got := strVal(m, "key", ""); got != "value" {
+		t.Errorf("strVal(key) = %q", got)
+	}
+	if got := strVal(m, "missing", "def"); got != "def" {
+		t.Errorf("strVal(missing) = %q", got)
+	}
+}
+
+func TestBoolVal(t *testing.T) {
+	m := map[string]any{"flag": true, "str": "not-bool"}
+	if got := boolVal(m, "flag", false); !got {
+		t.Error("boolVal(flag) should be true")
+	}
+	if got := boolVal(m, "str", false); got {
+		t.Error("boolVal(str) should be false (not a bool)")
+	}
+	if got := boolVal(m, "missing", true); !got {
+		t.Error("boolVal(missing) should use fallback true")
+	}
+}
+
+func TestIntVal(t *testing.T) {
+	m := map[string]any{"int": 5, "float": 3.14, "int64": int64(99)}
+	if got := intVal(m, "int", 0); got != 5 {
+		t.Errorf("intVal(int) = %d", got)
+	}
+	if got := intVal(m, "float", 0); got != 3 {
+		t.Errorf("intVal(float) = %d", got)
+	}
+	if got := intVal(m, "int64", 0); got != 99 {
+		t.Errorf("intVal(int64) = %d", got)
+	}
+	if got := intVal(m, "missing", 42); got != 42 {
+		t.Errorf("intVal(missing) = %d", got)
+	}
+}
+
+func TestGetEnvHelpers(t *testing.T) {
+	t.Setenv("CHAT_TEST", "hello")
+	if got := getEnv("CHAT_TEST", "x"); got != "hello" {
+		t.Errorf("getEnv = %q", got)
+	}
+	if got := getEnv("NO_SUCH_VAR", "x"); got != "x" {
+		t.Errorf("getEnv fallback = %q", got)
+	}
+
+	t.Setenv("CHAT_PORT", "9090")
+	if got := getEnvInt("CHAT_PORT", 0); got != 9090 {
+		t.Errorf("getEnvInt = %d", got)
+	}
+	if got := getEnvInt("NO_SUCH_VAR", 80); got != 80 {
+		t.Errorf("getEnvInt fallback = %d", got)
+	}
+
+	t.Setenv("CHAT_FLAG", "true")
+	if got := getEnvBool("CHAT_FLAG", false); !got {
+		t.Error("getEnvBool should be true")
+	}
+	if got := getEnvBool("NO_SUCH_VAR", false); got {
+		t.Error("getEnvBool fallback should be false")
+	}
+}
+
+func TestMainBinaryBuilds(t *testing.T) {
+	// Verify the binary exists after build
+	if _, err := os.Stat("main.go"); err != nil {
+		t.Skip("main.go not found")
+	}
+}