fix(version): remove git subprocess fallback to prevent contention

Under high concurrency (17+ sessions), each bd version spawning git
processes causes severe contention and timeouts. Remove the runtime
git symbolic-ref fallback - branch info is nice-to-have but not essential.

Fixes: GH#503

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

cmd/bd/version.go

@@ -1,11 +1,9 @@
 package main
 
 import (
-	"context"
 	"fmt"
 	"os"
 	"runtime/debug"
-	"strings"
 
 	"github.com/spf13/cobra"
 	"github.com/steveyegge/beads/internal/beads"
@@ -150,17 +148,10 @@ func resolveBranch() string {
 		}
 	}
 
-	// Fallback: try to get branch from git at runtime
-	// Use symbolic-ref to work in fresh repos without commits
-	// Uses CWD repo context since this shows user's current branch
-	if rc, err := beads.GetRepoContext(); err == nil {
-		cmd := rc.GitCmdCWD(context.Background(), "symbolic-ref", "--short", "HEAD")
-		if output, err := cmd.Output(); err == nil {
-			if branch := strings.TrimSpace(string(output)); branch != "" && branch != "HEAD" {
-				return branch
-			}
-		}
-	}
+	// Note: We intentionally avoid a git subprocess fallback here.
+	// Under high concurrency (17+ sessions), each bd version spawning git
+	// processes causes severe contention and timeouts. Branch info is
+	// nice-to-have but not essential for version output.
 
 	return ""
 }