fix(update): use server-side status endpoint instead of GitHub API from browser

[gnacho]

Problem

Both UpdateRibbon.tsx and the check button in Ajustes.tsx were fetching the latest release directly from github.com/ghapi in the browser. This causes GitHub rate-limit errors (403) on shared IPs (60 req/h unauthenticated), silently degrading to 'no updates available' with no user feedback.

The backend already had a proper server-side cached endpoint (GET /api/update/status) with a 5-minute kv cache, but the frontend was not using it.

Fix

• UpdateRibbon.tsx: replaced direct github.com/ghapi fetch with apiFetch('/api/update/status'). The endpoint returns { current, latest, available } from the server-side cache. Removed the now-unused compareSemver helper and pkg import.
• Ajustes.tsx checkUpdates: same fix - replaced the github.com/ghapi call (including the fallback to /tags) with the server-side endpoint. Removed the dead compareSemver function.

Result

-50 lines of duplicated GitHub API logic, +10 lines using the existing cached endpoint. The frontend no longer hits github.com/ghapi at all - all update checks go through the server, which rate-limits itself via the kv cache (5 min TTL).

Verified

• npm run build (vite): OK
• npm test (vitest): 105/105 passed
• eslint: 0 errors on touched files