perf(notifications): refresh enriched details when window regains focus

[afonsojramos]

Follow-up to #3102, implementing the approach proposed in #3102 (comment).

Problem

The enrichment cache introduced in #3102 is keyed by account:id:updatedAt, and some subject changes (labels, milestones, reactions) never bump a notification's updatedAt. Those details can therefore drift while the app polls in the background, with nothing to invalidate them until the thread next has real activity.

Change

Bust the enrichment cache when the Gitify window regains focus, so:

• the cache keeps saving API calls while the app polls in the background (where staleness is invisible),
• the moment the user actually views the inbox, every visible notification is re-enriched and up to date.

Implementation:

• New refreshEnrichmentCache(throttleMs) clears the cache and reports whether it did, throttled so rapid window open/close cycles cost at most one extra enrichment pass per throttle window (the fetch interval).
• The singleton side-effects host subscribes to TanStack's focusManager (the same signal that already drives refetchOnWindowFocus) and, when the cache was actually cleared, triggers an explicit refetch(). The explicit refetch matters because the built-in focus refetch is stale-gated (30s staleTime against a 60s default poll), so roughly half of focus events would otherwise not re-enrich until the next poll; when both fire, TanStack dedupes the concurrent fetches.
• Ordering is guaranteed: the cache clear runs synchronously within the focus dispatch, while any refetch only reads the cache after its own awaits (TanStack's focus handler additionally awaits before refetching). If those internals ever changed, the degradation is one stale interval, never incorrect data.

Tests

• notifications.test.ts: fake-timer coverage for clear, throttle, and throttle expiry.
• useNotifications.test.tsx: the side-effects host refreshes on window focus with the configured interval; plain consumers do not.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud