feat: add tier and session_log MCP tools

Adds two new MCP skill packages:
- internal/skills/org: exposes the tier tool, calling an injected TierFn
  for testability; returns current operating tier as structured JSON
- internal/skills/sessionlog: exposes the session_log tool, appending
  structured JSONL entries to brain/sessions/{session_id}.jsonl; requires
  session_id, wraps internal/session.Append

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

internal/skills/org/handlers_test.go

@@ -0,0 +1,29 @@
+// internal/skills/org/handlers_test.go
+package org_test
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	"github.com/mathiasbq/supervisor/internal/skills/org"
+	"github.com/mathiasbq/supervisor/internal/tier"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestHandle_Tier_ReturnsTierInfo(t *testing.T) {
+	s := org.New(org.Config{
+		TierFn: func(ctx context.Context) tier.Info {
+			return tier.Info{Tier: tier.LANOnly, Label: "lan-only", ManagedAgents: false}
+		},
+	})
+	out, err := s.Handle(context.Background(), "tier", nil)
+	require.NoError(t, err)
+
+	var info tier.Info
+	require.NoError(t, json.Unmarshal(out, &info))
+	assert.Equal(t, tier.LANOnly, info.Tier)
+	assert.Equal(t, "lan-only", info.Label)
+	assert.False(t, info.ManagedAgents)
+}