perf: cache filtered collections and add equatable row views

Convert filteredJobs, filteredPastes, and filteredTickets from computed
properties to stored properties updated via didSet on their inputs. Each
update function guards with an equality check before assigning, so
@Observable skips the notification when the filtered result hasn't
changed — preventing list re-renders on auto-refresh when no visible
data has actually changed.

Add Equatable conformance to BuildRowView, PasteRowView, TicketRowView,
and SelectableTicketRow, and apply .equatable() at each ForEach call
site. When a list does re-render, SwiftUI now skips body evaluation for
rows whose model value is identical to the previous pass.

Implements: https://todo.sr.ht/~ccleberg/hutch/57

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