fix(studio): show failures and empty searches in the global asset view

[kohjunhao]

What

The global asset view now tells four situations apart: loading, a failed request, a successful empty cache, and a search that matches none of the cached assets. A failed request offers a "Try again" button.

Why

The view showed "No assets in the global cache yet" for an empty cache, a failed request and a search with no matches. A non-OK response was converted to { assets: [] }, a rejected request to [], and any empty filtered list fell through to the empty-cache message, so users were told their cache was empty when the data was unavailable or only filtered out.

Related work

Fixes #4385 (approach posted on the issue first)

How

• One state value with three cases (loading, failed, loaded) replaces the nullable records array.
• A non-OK response throws into the existing catch, so both failure kinds land in failed.
• "Try again" sets loading and re-runs the fetch effect. Nothing retries on its own.
• "No global assets match" shows only when the request succeeded with records and the search filtered all of them out. Clearing the search restores the rows from memory without a new request.
• The successful-response handling and the existing empty-cache guidance are unchanged.

Test plan

• Unit tests added/updated
• Manual testing performed
• Documentation updated (if applicable)
• Comments follow CONTRIBUTING.md "Comments"

GlobalAssetsView.test.tsx uses controlled fetch responses. Five of its six cases fail on main, showing the empty-cache text for an error status, a rejected request and an unmatched search, and finding no way to retry.

bun run --cwd packages/studio test src/components/sidebar/GlobalAssetsView.test.tsx
bun run --cwd packages/studio test        (630 files, 6,934 tests pass on Node 22)
bun run --cwd packages/studio typecheck
bun run lint
bun run format:check
bunx fallow audit --base origin/main --fail-on-issues