New web UI for browsing vault history. Svelte + Vite app with components
for activity feed, dashboard, document detail, diff view, file tree,
header, login, time slider, toast container, vault picker; lib/api.ts and
stores.svelte.ts for client state. (Generated TS types were added in
PR6.)
Auto-generated TS types regenerated from Rust ts-rs derives, mirrored into
frontend/sync-client/src/services/types/ and frontend/history-ui/src/lib/types/.
Adds ListVaultsResponse, VaultHistoryResponse, VaultInfo and updates several
existing types; removes DeleteDocumentVersion and UpdateDocumentVersion.
