fix(timezone): default to UTC instead of browser timezone

[drankou]

When a user has no saved timezone preference, the dashboard now falls back to UTC instead of auto-detecting and persisting the browser's local timezone.

• Removed the effect that detected and saved the browser timezone on first load.
• The provider fallback stays DEFAULT_TIMEZONE (UTC), both server- and client-side.
• Users can still opt into their browser timezone via the "Use browser timezone" button in Account → Timezone settings.

🤖 Generated with Claude Code

[vercel]

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Project	Deployment	Actions	Updated (UTC)
web-foxtrot	Ready	Preview, Comment	Jul 14, 2026 2:32pm

[claude]

LGTM — straightforward removal of the auto-detect-and-persist effect, falling back to UTC as intended.

What was reviewed: the removed effect's only side effects (setTimezoneState/persistTimezone) are cleanly deleted with no dangling references; confirmed getBrowserTimezone remains used elsewhere (time-range-picker, account timezone settings' "Use browser timezone" button) so removing the import here doesn't break those; the provider still falls back to DEFAULT_TIMEZONE (UTC) for both initial state and SSR.

Extended reasoning...

Overview

Single-file change in src/features/dashboard/timezone/context.tsx that removes a useEffect which previously auto-detected the browser's timezone on first load and persisted it via a POST to /api/timezone/state. The provider now simply keeps the UTC default when no saved preference exists, matching the PR title/description.

Security risks

None. This only changes client-side default behavior for displaying timestamps; no auth, permissions, or data exposure surface is touched.

Level of scrutiny

Low. The diff is a pure deletion of an effect (net -9 lines), no new logic introduced, no new API surface, and the removed code path's only consumer (persist + local state) is fully deleted together — no orphaned references.

Other factors

Verified getBrowserTimezone is still imported and used by timezone-settings.tsx (the opt-in "Use browser timezone" button) and by time-range-picker.logic.ts, so the PR doesn't silently break those flows. No outstanding review comments in the timeline; only a Vercel bot preview-deployment comment.