feat(management): extract repository management into dashboard component

Move the inline repository management UI into a new RepositoryDashboard component
and wire it into the application. Refactor app state to compute a reactive
dashboardRepos list and update tab-closing logic so tabs can be closed while
preserving the management view when appropriate.

- Add a full dashboard with search, categories, workspaces and persisted prefs.
- Refactor close behavior to support keeping the management view open.
- Improve UI/CSS and accessibility for the management tab (compact layout and label).

src/lib/RepoTabs.svelte

@@ -27,6 +27,7 @@
     onclick={onOpenManagement}
     disabled={isBusy}
     title={language === "de" ? "Repository-Verwaltung" : "Repository Management"}
+    aria-label={language === "de" ? "Repository-Verwaltung" : "Repository Management"}
   >
     <Folder size={15} aria-hidden="true" />
   </button>