Expand one-of keys to multiple completion items (#261)

* Expand one-of keys to multiple completion items

Some workflow fields accept multiple YAML structures (scalar, sequence, or
mapping), but completions previously only showed a single option—leaving users
unaware of the full schema flexibility. This change surfaces structural options
and inserts the correct YAML scaffolding so users land in the right place to
keep typing.

Example: runs-on

Completing runs-on now shows three options:
- runs-on         → Ready for a string like ubuntu-latest
- runs-on (list)  → Ready to add runner labels
- runs-on (full syntax) → Ready for labels:, group:, etc.

Notes:
- Qualifiers (list) and (full syntax) only appear when multiple structural types exist
- Scalar completions use the plain key name
- Qualified variants use filterText matching the base key

* Sort expanded one-of completions: scalar, list, full syntax

languageservice/src/complete.ts

@@ -129,6 +129,8 @@ export async function complete(
 
     const item: CompletionItem = {
       label: value.label,
+      filterText: value.filterText,
+      sortText: value.sortText,
       documentation: value.description && {
         kind: "markdown",
         value: value.description
@@ -253,7 +255,7 @@ function getExpressionCompletionItems(
 
 function filterAndSortCompletionOptions(options: Value[], existingValues?: Set<string>) {
   options = options.filter(x => !existingValues?.has(x.label));
-  options.sort((a, b) => a.label.localeCompare(b.label));
+  options.sort((a, b) => (a.sortText ?? a.label).localeCompare(b.sortText ?? b.label));
   return options;
 }