refactor(completion): name path arguments explicitly and share firstArg

The six commands that take a file or directory argument set their
completer directly instead of a Use-line parser wrapping every
command, the first-argument-only wrappers become one firstArg helper,
and only the bash completion help keeps a custom text.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/metadata.go

@@ -161,7 +161,7 @@ $ tea milestone view 3 --web`, Annotations: map[string]string{"tea.arguments": m
 	}}
 	cmd.Flags().BoolVar(&byName, "by-name", false, "Match a numeric argument as a milestone title rather than an ID")
 	cmd.Flags().BoolVarP(&web, "web", "w", false, "Open the milestone in the browser")
-	cmd.ValidArgsFunction = a.completeMilestoneArgs(false)
+	cmd.ValidArgsFunction = firstArg(a.completeMilestones())
 	return cmd
 }
 
@@ -340,7 +340,7 @@ $ tea milestone edit 3 --editor`, Annotations: map[string]string{"tea.arguments"
 	}}
 	fields.register(cmd)
 	cmd.Flags().BoolVar(&byName, "by-name", false, "Match a numeric argument as a milestone title rather than an ID")
-	cmd.ValidArgsFunction = a.completeMilestoneArgs(false)
+	cmd.ValidArgsFunction = firstArg(a.completeMilestones())
 	return cmd
 }
 
@@ -367,7 +367,7 @@ $ tea milestone delete 7 --yes`, Annotations: map[string]string{"tea.confirm": "
 		return a.jsonResult(cmd, item)
 	}}
 	cmd.Flags().BoolVar(&byName, "by-name", false, "Match a numeric argument as a milestone title rather than an ID")
-	cmd.ValidArgsFunction = a.completeMilestoneArgs(false)
+	cmd.ValidArgsFunction = firstArg(a.completeMilestones())
 	return cmd
 }
 
@@ -378,15 +378,3 @@ func findMilestone(cmd *cobra.Command, s services.Milestones, raw string, byName
 	}
 	return s.FindOne(cmd.Context(), raw, byName)
 }
-
-// completeMilestoneArgs completes milestone titles for the first argument, or for every argument
-// when variadic.
-func (a *application) completeMilestoneArgs(variadic bool) cobra.CompletionFunc {
-	complete := a.completeMilestones()
-	return func(cmd *cobra.Command, args []string, toComplete string) ([]cobra.Completion, cobra.ShellCompDirective) {
-		if len(args) > 0 && !variadic {
-			return nil, cobra.ShellCompDirectiveNoFileComp
-		}
-		return complete(cmd, args, toComplete)
-	}
-}