Fix bd-1: Prevent test database pollution

Tests were connecting to test daemon but daemon routed to production DB via
findDatabaseForCwd(). Fixed by ensuring tests use isolated .beads directories
and change working directory to tmpDir.

Changes:
- bench_test.go: Added .beads subdir, chdir, and client.dbPath to setupBenchServer
- bench_test.go: Set dbPath for goroutine clients in BenchmarkConcurrentAgents
- comments_test.go: Refactored to use setupTestServer
- version_test.go: Fixed 4 tests to use setupTestServerIsolated with proper isolation
- rpc_test.go: Added setupTestServerIsolated() helper for custom test setup

Verified: RPC test suite runs with no database pollution (151→151 issues)
Amp-Thread-ID: https://ampcode.com/threads/T-348b7ba8-4292-4ed3-b143-0ad07d226c21
Co-authored-by: Amp <amp@ampcode.com>

internal/rpc/comments_test.go

@@ -1,51 +1,15 @@
 package rpc
 
 import (
-	"context"
 	"encoding/json"
-	"path/filepath"
 	"testing"
-	"time"
 
-	sqlitestorage "github.com/steveyegge/beads/internal/storage/sqlite"
 	"github.com/steveyegge/beads/internal/types"
 )
 
 func TestCommentOperationsViaRPC(t *testing.T) {
-	tmpDir := t.TempDir()
-	dbPath := filepath.Join(tmpDir, "test.db")
-	socketPath := filepath.Join(tmpDir, "bd.sock")
-
-	store, err := sqlitestorage.New(dbPath)
-	if err != nil {
-		t.Fatalf("failed to create store: %v", err)
-	}
-	defer store.Close()
-
-	server := NewServer(socketPath, store)
-
-	ctx, cancel := context.WithCancel(context.Background())
-	serverErr := make(chan error, 1)
-	go func() {
-		serverErr <- server.Start(ctx)
-	}()
-
-	select {
-	case <-server.WaitReady():
-	case err := <-serverErr:
-		t.Fatalf("server failed to start: %v", err)
-	case <-time.After(2 * time.Second):
-		t.Fatal("timeout waiting for server to start")
-	}
-
-	client, err := TryConnect(socketPath)
-	if err != nil {
-		t.Fatalf("failed to connect to server: %v", err)
-	}
-	if client == nil {
-		t.Fatal("client is nil after successful connection")
-	}
-	defer client.Close()
+	_, client, cleanup := setupTestServer(t)
+	defer cleanup()
 
 	createResp, err := client.Create(&CreateArgs{
 		Title:     "Comment test",
@@ -98,16 +62,4 @@ func TestCommentOperationsViaRPC(t *testing.T) {
 	if comments[0].Text != "first comment" {
 		t.Fatalf("expected comment text 'first comment', got %q", comments[0].Text)
 	}
-
-	if err := server.Stop(); err != nil {
-		t.Fatalf("failed to stop server: %v", err)
-	}
-	cancel()
-	select {
-	case err := <-serverErr:
-		if err != nil && err != context.Canceled {
-			t.Fatalf("server returned error: %v", err)
-		}
-	default:
-	}
 }