Spike: expand useSearchParams for shareable/bookmarkable views

## Goal

Today only `DataExplorer` uses `useSearchParams` (paging). Filter/search state elsewhere lives in component/Jotai state and is lost on refresh and not shareable via URL. Investigate using `useSearchParams` to persist view state in the URL so views are bookmarkable and shareable — works in declarative mode, no router upgrade needed.

## Expected Outcome

Inventory of view state that would benefit (filters, search, selected types, etc.), a recommendation on which to URL-encode, and the UX/product implications (e.g. hash-based sharing). Task out follow-up work if worthwhile.

> [!IMPORTANT]
> Internal only — this issue is maintained by the core team and is not accepting external contributions.

Start with DataExplorer and its existing useSearchParams usage to understand the current paging behavior. Inventory the filter, search, and selected-type state held in components or Jotai, then assess which state could be URL-encoded in declarative mode. Done means a documented inventory, recommendation, UX implications, and follow-up tasks where appropriate.

Written by the indexing model from the issue text.