feat(ui): standardize loading and empty states across primary data pages

[Favouromale]

Summary

Closes #29

Wires up the existing EmptyState / Skeleton component primitives (already built under src/components/EmptyState and src/components/Skeleton, but not consumed anywhere outside Storybook) into the primary data pages, so each shows a shape-matching loading skeleton and a friendly empty state instead of a blank panel, a bare spinner, or ad-hoc placeholder text.

Pages updated

• Bridges (src/pages/Bridges.tsx) — swapped the ad-hoc empty <div>s for EmptyBridges, wired to the favorites toggle and bridge status filter.
• Watchlist (src/pages/Watchlist.tsx) — swapped the inline empty block for EmptyWatchlist; added SkeletonText to the price/health table cells while per-asset stats are loading.
• Alerts (src/components/alerts/CompactAlertList.tsx, rendered by Alerts.tsx) — distinguishes "no active alerts" from "no alerts match your filters/search" via EmptyAlerts, with a clear-filters action that resets severity/status/search/dismissed state.
• Incidents (src/components/IncidentHeatmap.tsx, rendered by Incidents.tsx) — replaced the plain "Loading…" text with a skeleton grid matching the heatmap's shape, and added a new EmptyIncidents variant for the zero-incidents case.
• Transactions (src/components/TransactionHistory.tsx, rendered by Transactions.tsx) — replaced the duplicated desktop/mobile empty blocks with EmptyTransactions, distinguishing a genuinely empty result set from an active-filter mismatch.

Empty vs. no-matches

EmptyBridges, EmptyAlerts, and EmptyTransactions now accept a hasFilters / onClearFilters pair so "nothing here yet" is visually and textually distinct from "nothing matches your current filter", with a "Clear filters" action for the latter case.

i18n

All empty-state copy consumed by these pages now runs through react-i18next (new emptyStates.* keys plus common.clearFilters), translated across all 8 supported locales (en, es, fr, de, zh, ja, ko, ar) to keep src/i18n/localeCompleteness.test.ts green.

Reduced motion

The .skeleton shimmer animation is already gated globally in src/index.css (@media (prefers-reduced-motion: reduce) zeroes all animation/transition durations), so no additional per-component work was needed for this criterion — new skeleton markup reuses the same .skeleton class.

Tests

• src/components/EmptyState/variants.test.tsx — covers the empty vs. filtered rendering (and copy) of EmptyBridges, EmptyAlerts, EmptyIncidents, EmptyTransactions, EmptyWatchlist.
• src/pages/Watchlist.test.tsx — covers the Watchlist page's empty state and its disappearance once an asset is added.

Testing/validation performed

• npx tsc -p tsconfig.json --noEmit — passes
• npx eslint src/ --ext .ts,.tsx — passes, no warnings
• npx vitest run — full suite passes: 611 tests / 58 files, including the locale-completeness test across all 8 locales
• npm run build — production build succeeds

Notes / follow-ups

• Scope matches the issue: only the 5 listed primary pages were touched. Other pages using ad-hoc empty/loading states are explicitly out of scope per the issue ("future-batch work").
• package-lock.json had a pre-existing local diff unrelated to this change (a storybook addon version) and was intentionally left out of this PR.