Reduce redundant GitHub API calls when polling notifications

[joshfree]

The problem

On every poll, Gitify re-fetches data it already has:

1. Re-enriches every notification, even unchanged ones. For N visible notifications, getAllNotifications → enrichNotifications (src/renderer/utils/notifications/notifications.ts) issues ceil(N / 100) GraphQL detail queries every interval, with no change detection (enrich.ts, GITHUB_API_MERGE_BATCH_SIZE = 100).
2. Disables caching on the list request. listNotificationsForAuthenticatedUser (client.ts) sets Cache-Control: no-cache, so the full notifications list is re-downloaded every poll even when nothing changed.

For someone watching busy repos, nearly every request each minute is redundant.

Why fixing it helps

GitHub's API makes the "nothing changed" case almost free — Gitify just isn't using the mechanisms:

• Conditional requests (If-Modified-Since / If-None-Match) return 304 Not Modified with an empty body, and 304s don't count against the rate limit.
• X-Poll-Interval tells clients the minimum safe poll spacing.

Adopting these turns the common steady-state poll from "re-download the whole list + re-fetch every notification" into "one conditional request that returns 304, zero detail fetches." Result: much lower API/
rate-limit usage and bandwidth, fewer throttled requests, and no change to user-visible behavior. This especially helps heavy users and anyone running multiple accounts.

Proposed fixes (independent, in priority order)

1. Skip re-enriching unchanged notifications. Cache the enriched subject keyed by account + id + updatedAt; reuse it when updatedAt is unchanged, only fetching cache misses. Prune to current
   notifications each cycle. Forge-agnostic — lives in the enrichment orchestrator.
2. Conditional requests on the list. Drop Cache-Control: no-cache, send If-Modified-Since/If-None-Match, store the returned Last-Modified/ETag per account, and reuse the last list on 304. Localized to client.ts.
3. Respect X-Poll-Interval. Poll no more often than max(userInterval, X-Poll-Interval) (useNotifications.ts currently uses only the fixed fetchIntervalMs).

References

• Best practices for using the REST API
• Rate limits (conditional requests don't count)
• List notifications for the authenticated user

Happy to open a PR for these.