GA-009: add available shifts filtering and sorting

[abrar-deakin]

Summary

• Added available shifts filtering by status.
• Added sorting by date and pay.
• Added date filters (Today / Next 7 Days / All).

Testing

• Created a shift from Employer Panel.
• Verified the shift appears in the Guard App.
• Successfully applied for the shift.
• Verified the status changes to Pending.
• Verified Employer receives the application notification.

Screenshots

Employer - Shift Created

Guard App - Available Shift

Guard App - Application Success

Employer - Notification Received

[Krisha190235]

Nice filter/sort/error-retry additions — I confirmed the status values match mapAllShifts output, so that filter's correct, and bumping the page size 20→50 is a good call.

One thing worth fixing before merge:

The search now matches title + site only — it dropped company, which mapAllShifts does populate, so guards lose the ability to search by company. Can we add it back (${shift.title} ${shift.company} ${shift.site}``) unless that was intentional?

Two non-blockers:

catch (err: any) just trips the no-explicit-any warning (it's set to warn, so CI stays green) — optional to switch to unknown + narrow for consistency with the other screens.
listShifts(1, 50) loads one page of 50 and filters/sorts client-side, since /shifts is paginated — fine for now (and better than the old 20), but worth a follow-up for load-more or server-side filtering so large lists stay reachable.

Otherwise LGTM once the company-search line is sorted.