feat: Normalize prefix by stripping trailing hyphens in bd init

Ensures exactly one hyphen between prefix and issue number regardless of
whether user provides trailing hyphen.

Before:
  bd init --prefix wy-  → Issues: wy--1, wy--2 (double hyphen)
  bd init --prefix wy   → Issues: wy-1, wy-2 (single hyphen)

After:
  bd init --prefix wy-  → Issues: wy-1, wy-2 (single hyphen)
  bd init --prefix wy   → Issues: wy-1, wy-2 (single hyphen)

The hyphen is added automatically during ID generation in CreateIssue(),
so the stored prefix should never include trailing hyphens.

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

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

cmd/bd/init.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/fatih/color"
 	"github.com/spf13/cobra"
@@ -28,6 +29,10 @@ and database file. Optionally specify a custom issue prefix.`,
 			prefix = filepath.Base(cwd)
 		}
 
+		// Normalize prefix: strip trailing hyphens
+		// The hyphen is added automatically during ID generation
+		prefix = strings.TrimRight(prefix, "-")
+
 		// Create .beads directory
 		beadsDir := ".beads"
 		if err := os.MkdirAll(beadsDir, 0750); err != nil {