fix: usage week aligns with UTC calendar week (#875)

[ionfwsrijan]

Problem

Usage XP windows used a rolling 7x24-hour window that did not match the database's date_trunc('week') grouping, so award totals, grouping, and cleanup could disagree about which "week" a contribution belonged to ? especially at week boundaries.

Fix

• The usage week now aligns with the UTC calendar week: it starts at the Monday 00:00 UTC boundary computed via Date.UTC(now.getUTCFullYear(), now.getUTCMonth(), now.getUTCDate() - daysSinceMonday), matching date_trunc('week').

Files changed

• src/app/actions/usage.ts
• Tests (usage actions + regression boundary test)

Testing

• Full MergeShip suite passes.
• New regression test pins the boundary between calendar weeks.

Closes #875

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[github-actions]

Hey @ionfwsrijan

You have 7 open PRs right now. The limit is 3 at a time.

Please get your existing PRs merged or closed before opening new ones:

• fix: revoke stale per-repo grants (#874) #879 - fix: revoke stale per-repo grants ([BUG] Revoked per-repo maintainer grants are never cleaned up — installation_user_repos rows persist forever after a collaborator is demoted #874)
• fix: prevent self-merge recommended-XP loop (#873) #878 - fix: prevent self-merge recommended-XP loop ([BUG] Recommended-merge XP has no self-merge guard — a repo owner can claim and merge their own repo's issues for up to 400 XP, bypassing the anti-abuse rule enforced on unrecommended merges #873)
• fix: reconcile merged-PR XP across all installs and pages (#872) #877 - fix: reconcile merged-PR XP across all installs and pages ([BUG] reconcileMergedPrXp never scans beyond the first 50 installs, first 20 repos, or the first 100 closed PRs — lost merge XP is permanently unrecoverable on busy repos #872)
• fix: exact maintainer status check with negative-cache lockdown (#871) #876 - fix: exact maintainer status check with negative-cache lockdown ([BUG] isUserMaintainer truncates the grant check to 20 junction rows and caches the result for 1h — maintainers with many installs are wrongly locked out #871)
• fix: maintainer queue pagination with in-SQL filters and exact counts #868 - fix: maintainer queue pagination with in-SQL filters and exact counts

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[ionfwsrijan]

@jakharmonika364 @Soumya-codr Please review this

[jakharmonika364]

Cheers! LGTM