feat: add integration branch management for swarms

- CreateIntegrationBranch: create from BaseCommit, push to origin
- MergeToIntegration: merge worker branch with conflict detection
- LandToMain: merge integration to target branch
- CleanupBranches: remove all swarm branches after landing
- Helper functions for branch naming conventions

Closes gt-kmn.3

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/swarm/integration_test.go

@@ -0,0 +1,106 @@
+package swarm
+
+import (
+	"testing"
+
+	"github.com/steveyegge/gastown/internal/rig"
+)
+
+func TestGetIntegrationBranch(t *testing.T) {
+	r := &rig.Rig{
+		Name: "test-rig",
+		Path: "/tmp/test-rig",
+	}
+	m := NewManager(r)
+
+	swarm, _ := m.Create("epic-1", []string{"Toast"}, "main")
+
+	branch, err := m.GetIntegrationBranch(swarm.ID)
+	if err != nil {
+		t.Fatalf("GetIntegrationBranch failed: %v", err)
+	}
+
+	expected := "swarm/epic-1"
+	if branch != expected {
+		t.Errorf("branch = %q, want %q", branch, expected)
+	}
+}
+
+func TestGetIntegrationBranchNotFound(t *testing.T) {
+	r := &rig.Rig{
+		Name: "test-rig",
+		Path: "/tmp/test-rig",
+	}
+	m := NewManager(r)
+
+	_, err := m.GetIntegrationBranch("nonexistent")
+	if err != ErrSwarmNotFound {
+		t.Errorf("GetIntegrationBranch = %v, want ErrSwarmNotFound", err)
+	}
+}
+
+func TestGetWorkerBranch(t *testing.T) {
+	r := &rig.Rig{
+		Name: "test-rig",
+		Path: "/tmp/test-rig",
+	}
+	m := NewManager(r)
+
+	branch := m.GetWorkerBranch("sw-1", "Toast", "task-123")
+	expected := "sw-1/Toast/task-123"
+	if branch != expected {
+		t.Errorf("branch = %q, want %q", branch, expected)
+	}
+}
+
+func TestCreateIntegrationBranchSwarmNotFound(t *testing.T) {
+	r := &rig.Rig{
+		Name: "test-rig",
+		Path: "/tmp/test-rig",
+	}
+	m := NewManager(r)
+
+	err := m.CreateIntegrationBranch("nonexistent")
+	if err != ErrSwarmNotFound {
+		t.Errorf("CreateIntegrationBranch = %v, want ErrSwarmNotFound", err)
+	}
+}
+
+func TestMergeToIntegrationSwarmNotFound(t *testing.T) {
+	r := &rig.Rig{
+		Name: "test-rig",
+		Path: "/tmp/test-rig",
+	}
+	m := NewManager(r)
+
+	err := m.MergeToIntegration("nonexistent", "branch")
+	if err != ErrSwarmNotFound {
+		t.Errorf("MergeToIntegration = %v, want ErrSwarmNotFound", err)
+	}
+}
+
+func TestLandToMainSwarmNotFound(t *testing.T) {
+	r := &rig.Rig{
+		Name: "test-rig",
+		Path: "/tmp/test-rig",
+	}
+	m := NewManager(r)
+
+	err := m.LandToMain("nonexistent")
+	if err != ErrSwarmNotFound {
+		t.Errorf("LandToMain = %v, want ErrSwarmNotFound", err)
+	}
+}
+
+func TestCleanupBranchesSwarmNotFound(t *testing.T) {
+	r := &rig.Rig{
+		Name: "test-rig",
+		Path: "/tmp/test-rig",
+	}
+	m := NewManager(r)
+
+	err := m.CleanupBranches("nonexistent")
+	if err != ErrSwarmNotFound {
+		t.Errorf("CleanupBranches = %v, want ErrSwarmNotFound", err)
+	}
+}