feat(updates): add View changelog button to settings

[charlesvien]

Problem

There was no way to view the release changelog from Settings. The "What's New" changelog (full release history) was only reachable from the project switcher menu, so a user looking at their current version in Settings → Updates had no path to see what changed.

Changes

Added a View changelog button to the left of the current-version badge in Settings → Updates. It opens the existing WhatsNewModal (release history grouped by day/week, with "Latest" and "Current" badges marking the version you're on).

• Reuses the existing useWhatsNewStore.getState().open() pattern already used by ProjectSwitcher's "View changelog" menu item, so behavior is consistent.
• The WhatsNewModal is already mounted on the settings route, so no extra wiring was needed.
• Button and Flex were already imported in UpdatesSettings.tsx; only the useWhatsNewStore import was added.

How did you test this?

• pnpm typecheck (full monorepo, via the pre-commit hook) — passed
• pnpm --filter @posthog/ui typecheck — passed
• biome check on the changed file (via the pre-commit hook) — passed

No screenshot attached: this worktree can't launch the packaged Electron app, so I couldn't capture the running UI. The change is a small ghost-style View changelog button placed to the left of the existing current-version badge in Settings → Updates; clicking it opens the already-built What's New modal (release history grouped by day/week). No new modal or layout was introduced.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 6c28361.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "add view changelog button to update sett..." | Re-trigger Greptile}

[github-actions]

Simple additive UI change — adds a "View changelog" button in the settings update row. No business logic, no API changes, no data model impact.