[web-shared]: fix event payload loading (e.g. step_created)

[karthikscale3]

PR description

What

• event-list-view: Reworks when event details load and how they’re merged. Applies cached rows into local state, guards concurrent loads with isLoading, and prefers the fully loaded payload over inline list eventData when both exist. While a fetch is in flight, the UI can keep showing the last known payload instead of blanking out.
• events-list (sidebar): Uses the same display rule—loadedData overrides existingData so list snippets don’t block or replace fetched details. Skips duplicate fetches when a payload is already loaded (via a ref-backed guard). On encryption key changes, clears cache and forces a refetch so loadEventData isn’t stuck behind a stale loadedData !== null closure. hasOnlyExpiredFields now uses EVENT_DATA_REF_FIELDS so “all expired” only considers ref/payload keys for that eventType (not a fixed list for every type).
• hydration (web-shared): Replaces the hardcoded eventData key list with EVENT_DATA_REF_FIELDS for encrypted/expired markers and decrypt paths, only touching keys that exist on the object—aligned with world’s per-event ref fields and avoids touching irrelevant keys.

Why

List APIs often return partial or stale eventData. The old merge order and early returns could prevent or override a full fetch (notably for step_created). These changes make the timeline and sidebar fetch-first, keep loading UX stable, fix decrypt-after-key reloads, and keep serialization / expiry handling scoped to the fields that actually exist for each event type.

[ghost]

Backported to stable (38a642b -> d210a59).