feat: add tier detection package

Probes Anthropic and LiteLLM endpoints to detect the current operating
tier (Full / LANOnly / Airplane) so downstream code can gate model
selection and managed-agent availability without manual configuration.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/tier/tier_test.go

@@ -0,0 +1,48 @@
+// internal/tier/tier_test.go
+package tier_test
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/mathiasbq/supervisor/internal/tier"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDetect_Tier1_WhenBothReachable(t *testing.T) {
+	anthropic := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer anthropic.Close()
+
+	litellm := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer litellm.Close()
+
+	info := tier.Detect(context.Background(), anthropic.URL, litellm.URL)
+	assert.Equal(t, tier.Full, info.Tier)
+	assert.Equal(t, "full-online", info.Label)
+	assert.True(t, info.ManagedAgents)
+}
+
+func TestDetect_Tier2_WhenOnlyLiteLLMReachable(t *testing.T) {
+	litellm := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer litellm.Close()
+
+	info := tier.Detect(context.Background(), "http://127.0.0.1:1", litellm.URL)
+	assert.Equal(t, tier.LANOnly, info.Tier)
+	assert.Equal(t, "lan-only", info.Label)
+	assert.False(t, info.ManagedAgents)
+}
+
+func TestDetect_Tier3_WhenNeitherReachable(t *testing.T) {
+	info := tier.Detect(context.Background(), "http://127.0.0.1:1", "http://127.0.0.1:2")
+	assert.Equal(t, tier.Airplane, info.Tier)
+	assert.Equal(t, "airplane", info.Label)
+	assert.False(t, info.ManagedAgents)
+}