perf: switch refetchOnWindowFocus to staleTime-gated

[FrkAk]

Summary

Task Reference: [MYMR-222]

Switch lib/query/client.ts:17 from refetchOnWindowFocus: "always" to refetchOnWindowFocus: true so focus refetches respect the existing 30-second staleTime. The "always" value bypasses staleTime and triggers a full refetch on every tab-focus event regardless of whether the query is fresh; the regular true value gates focus refetches on staleTime. Combined with the conditional-GET path at lib/api/conditional.ts:42 (which emits ETags on slim project / task responses), refocus events inside the stale window become no-ops, and refocus events outside it still revalidate but collapse to ~50-byte 304s when the data has not changed.

This is the bridge stop-gap before MYMR-215 (Durable Object WebSocket push) lets us flip refetchOnWindowFocus: false entirely. Once push exists the client gets explicit invalidation messages and no longer needs focus-driven polling for liveness.

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Documentation

Testing

• Tested locally with bun run dev
• Linting passes (bun run lint)
• Typecheck passes (bun run typecheck)

Notes for reviewer

• One-line change. No tests, no types, no API surface.
• Manual verification after deploy: open the workspace view, switch tab focus 10x over 5 minutes without making any data changes, observe 304 responses for /api/projects/* GETs in the DevTools network panel instead of 200 with full bodies.
• Data freshness invariants still hold: staleTime gates focus refetch, ETag revalidation runs on stale-window expiry.