Add prefix validation to prevent wrong-database issue creation

Closes bd-156 (originally bd-151, remapped during auto-import)

Validates that explicit --id prefix matches database prefix from config.
Prevents accidental creation of issues with wrong prefix (e.g., creating
'bd-118' in a database configured for 'vc-' prefix).

Features:
- Checks issue_prefix from config table when --id is provided
- Fails with helpful error message showing the mismatch
- Suggests correct prefix format
- Adds --force flag to override validation if intentional
- Only validates in direct mode (daemon needs RPC enhancement)

Example: bd create 'Test' --id vc-99  # Error: prefix mismatch, use bd-99
  bd create 'Test' --id vc-99 --force  # OK, forced override
Amp-Thread-ID: https://ampcode.com/threads/T-4e1ac6f1-7465-442a-a385-adaa98b539ad
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/main.go

@@ -960,6 +960,7 @@ var createCmd = &cobra.Command{
 		explicitID, _ := cmd.Flags().GetString("id")
 		externalRef, _ := cmd.Flags().GetString("external-ref")
 		deps, _ := cmd.Flags().GetStringSlice("deps")
+		forceCreate, _ := cmd.Flags().GetBool("force")
 
 		// Validate explicit ID format if provided (prefix-number)
 		if explicitID != "" {
@@ -974,6 +975,30 @@ var createCmd = &cobra.Command{
 				fmt.Fprintf(os.Stderr, "Error: invalid ID format '%s' (numeric suffix required, e.g., 'bd-42')\n", explicitID)
 				os.Exit(1)
 			}
+			
+			// Validate prefix matches database prefix (unless --force is used)
+			if !forceCreate {
+				requestedPrefix := parts[0]
+				ctx := context.Background()
+				
+				// Get database prefix from config
+				var dbPrefix string
+				if daemonClient != nil {
+					// Using daemon - need to get config via RPC
+					// For now, skip validation in daemon mode (needs RPC enhancement)
+				} else {
+					// Direct mode - check config
+					dbPrefix, _ = store.GetConfig(ctx, "issue_prefix")
+				}
+				
+				if dbPrefix != "" && dbPrefix != requestedPrefix {
+					fmt.Fprintf(os.Stderr, "Error: prefix mismatch detected\n")
+					fmt.Fprintf(os.Stderr, "  This database uses prefix '%s-', but you specified '%s-'\n", dbPrefix, requestedPrefix)
+					fmt.Fprintf(os.Stderr, "  Did you mean to create '%s-%s'?\n", dbPrefix, parts[1])
+					fmt.Fprintf(os.Stderr, "  Use --force to create with mismatched prefix anyway\n")
+					os.Exit(1)
+				}
+			}
 		}
 
 		var externalRefPtr *string
@@ -1116,6 +1141,7 @@ func init() {
 	createCmd.Flags().String("id", "", "Explicit issue ID (e.g., 'bd-42' for partitioning)")
 	createCmd.Flags().String("external-ref", "", "External reference (e.g., 'gh-9', 'jira-ABC')")
 	createCmd.Flags().StringSlice("deps", []string{}, "Dependencies in format 'type:id' or 'id' (e.g., 'discovered-from:bd-20,blocks:bd-15' or 'bd-20')")
+	createCmd.Flags().Bool("force", false, "Force creation even if prefix doesn't match database prefix")
 	rootCmd.AddCommand(createCmd)
 }