fix: wire workspace.skills into the sidebar + workspace-index gates (open-webui#24729)

Reported by bwgabrielsusai on open-webui#24719: granting a user only
`workspace.skills` doesn't show the Workspace menu, and visiting
`/workspace` directly bounces them to `/`.

The per-route guard in `/workspace/+layout.svelte` already covered
skills, but two earlier gates in the chain didn't:

* `Sidebar.svelte` case 'workspace' OR'd models/knowledge/prompts/tools
  to decide menu visibility — skills was missing, so the entry never
  rendered for skills-only users.
* `/workspace/+page.svelte` redirect chain picked the first available
  section — skills was missing, so the fallback `goto('/')` fired.

Adding skills to both.

Author: Classic298

src/lib/components/layout/Sidebar.svelte

@@ -119,7 +119,8 @@
 					$user?.permissions?.workspace?.models ||
 					$user?.permissions?.workspace?.knowledge ||
 					$user?.permissions?.workspace?.prompts ||
-					$user?.permissions?.workspace?.tools
+					$user?.permissions?.workspace?.tools ||
+					$user?.permissions?.workspace?.skills
 				);
 			case 'automations':
 				return (

src/routes/(app)/workspace/+page.svelte

@@ -13,6 +13,8 @@
 				goto('/workspace/prompts');
 			} else if ($user?.permissions?.workspace?.tools) {
 				goto('/workspace/tools');
+			} else if ($user?.permissions?.workspace?.skills) {
+				goto('/workspace/skills');
 			} else {
 				goto('/');
 			}