refactor: consolidate loading/error states and extract instance actions hook

Frontend:
- Create reusable DataStates components (LoadingState, ErrorState, EmptyState)
- Refactor 12 pages to use shared state components instead of inline JSX
- Extract useInstanceActions hook to eliminate session action duplication
- Update dashboard and sessions pages to use shared hook

OpenSpec:
- Archive completed mobile-app-usability change (44/44 tasks)
- Archive completed add-config-profiles change (15/15 tasks)

Quality: TypeScript check passes, production build succeeds

apps/web/src/pages/git-repositories.tsx

@@ -6,6 +6,7 @@ import {
   listRepositories,
 } from "../api/git_repositories";
 import type { GitRepository } from "../api/git_repositories";
+import { EmptyState, ErrorState, LoadingState } from "../components/data-states";
 import { Icon } from "../components/icon";
 import { RepositoryCreateDialog } from "../components/repository-create-dialog";
 import { useAsyncData } from "../hooks/use-async-data";
@@ -48,19 +49,11 @@ export const GitRepositoriesPage = () => {
         </button>
       </div>
 
-      {status === "loading" && <p className="muted">Loading repositories...</p>}
+      {status === "loading" && <LoadingState message="Loading repositories..." />}
 
-      {status === "error" && (
-        <div className="card stack">
-          <p>Failed to load repositories</p>
-          <button className="secondary-button" onClick={() => reload()} type="button">
-            <Icon name="refresh" size="sm" />
-            Retry
-          </button>
-        </div>
-      )}
+      {status === "error" && <ErrorState message="Failed to load repositories" onRetry={reload} />}
 
-      {isEmpty && <p className="muted">No repositories yet. Create your first repository above.</p>}
+      {isEmpty && <EmptyState message="No repositories yet. Create your first repository above." />}
 
       {status === "ready" && safeRepositories.length > 0 && (
         <div className="repository-list">