feat(cli): add 'gt show' command for inspecting beads

Desire path: agents naturally try 'gt show <id>' to inspect beads.
This wraps 'bd show' via syscall.Exec, passing all flags through.

- Works with any prefix (gt-, bd-, hq-, etc.)
- Routes to correct beads database automatically
- DisableFlagParsing passes all flags to bd show

Closes gt-82jxwx

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

internal/cmd/show.go

@@ -0,0 +1,57 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"syscall"
+
+	"github.com/spf13/cobra"
+)
+
+func init() {
+	showCmd.GroupID = GroupWork
+	rootCmd.AddCommand(showCmd)
+}
+
+var showCmd = &cobra.Command{
+	Use:   "show <bead-id> [flags]",
+	Short: "Show details of a bead",
+	Long: `Displays the full details of a bead by ID.
+
+Delegates to 'bd show' - all bd show flags are supported.
+Works with any bead prefix (gt-, bd-, hq-, etc.) and routes
+to the correct beads database automatically.
+
+Examples:
+  gt show gt-abc123          # Show a gastown issue
+  gt show hq-xyz789          # Show a town-level bead (convoy, mail, etc.)
+  gt show bd-def456          # Show a beads issue
+  gt show gt-abc123 --json   # Output as JSON
+  gt show gt-abc123 -v       # Verbose output`,
+	DisableFlagParsing: true, // Pass all flags through to bd show
+	RunE:               runShow,
+}
+
+func runShow(cmd *cobra.Command, args []string) error {
+	if len(args) == 0 {
+		return fmt.Errorf("bead ID required\n\nUsage: gt show <bead-id> [flags]")
+	}
+
+	return execBdShow(args)
+}
+
+// execBdShow replaces the current process with 'bd show'.
+func execBdShow(args []string) error {
+	bdPath, err := exec.LookPath("bd")
+	if err != nil {
+		return fmt.Errorf("bd not found in PATH: %w", err)
+	}
+
+	// Build args: bd show <all-args>
+	// argv[0] must be the program name for exec
+	fullArgs := append([]string{"bd", "show"}, args...)
+
+	// Replace process with bd show
+	return syscall.Exec(bdPath, fullArgs, os.Environ())
+}