Add unit coverage for use-activity

[selfcontained]

Summary

The activity hooks (apps/web/src/hooks/use-activity.ts) power the entire activity/stats pane but had zero direct test coverage. This adds use-activity.test.tsx (27 tests) covering the pure range logic and the query-hook wiring, closing the last item of the 2026-07-31 ranked web coverage queue.

What is pinned

• getRangeBounds, all five ranges: explicit daily date → local midnight through next local midnight; daily end lands on the next calendar midnight across a DST transition (2026-03-08), not start+24h; the default daily date is derived from the UTC date but parsed as local midnight (documented product quirk, pinned at an instant where the two disagree west of UTC); year starts at local Jan 1; 7d/30d are exact rolling epoch windows; all-time returns empty bounds.
• Granularity mapping through real request URLs: daily→hour, 7d/30d→day, year/all→month.
• Query-param construction: ambient tz always sent; start/end omitted entirely for all-time; useActiveHours sends raw bounds with no granularity param (distinct from the other endpoints).
• Payload unwrapping: heatmap→days, token-by-model→models, token-by-project / working-time-by-project→projects; four passthrough endpoints return the payload as-is.
• Query behavior: cache keyed per range + dailyDate; refetchOnMount: "always" refetches on remount while fresh.

All timezone assertions are written relative to the ambient zone (the module captures LOCAL_TZ at import), verified to hold in both America/Denver and UTC.

Validation

• 11/11 targeted mutant battery killed (granularity halves, dailyDate ignored, DST end bound, UTC-midnight year start, off-by-one window, bounds leaking into all-time, unconditional start param, un-unwrapped payload, granularity leaking into active-hours, hardcoded heatmap window, hardcoded tz).
• One review-agent round: 0 must-fix; 2 should-fix applied (exact ISO oracle for the daily-default test, explicit error in the calledUrl helper), 1 nit applied (dropped unnecessary casts).
• pnpm run check, full unit suite (server 2394 / web 617 / ext 60 / scripts 4), pnpm run finalize:web, inert E2E 175 passed / 12 skipped, live lane 11 passed — all green.

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