Phase 3: Svelte 5 UI skeleton

Svelte 5 + Vite + TypeScript dashboard that consumes kamado-api over
REST for the first paint and then subscribes to /api/ws for live
updates. Zero runtime deps beyond svelte itself; plain CSS, no
component library.

Layout:

- Header with brand, WebSocket status badge, chain + height
- PoolOverview: hashrate (1m/5m/1h/24h), miner count, network
  hashrate + diff, pool share (ppb), expected time to block, uptime
- BlocksTable: recent solves from the in-memory ring (will be
  SQLite-backed in Phase 2b.5)
- BestShares: top-10 workers by bestever, falling back to bestdiff
  when the ckpool patch isn't present
- MinersTable: joined view of stratum clients and workers with
  user-agent-based hardware detection (Bitaxe, NerdQAxe, Antminer,
  ...), hashrate, best-round, best-ever, last share

State is a single $state() snapshot store in svelte-runes form;
components read from it via $derived. The store does one initial
REST snapshot fetch, then owns the WebSocket with exponential
backoff reconnects.

Vite dev server on :5173 proxies /api and /api/ws to localhost:8080
so you can run `make ui-dev` alongside `make up` in development.
Production serving (bundled into the Go binary via embed, behind /
on :8080) lands in Phase 4.

ui/src/lib/BestShares.svelte

@@ -0,0 +1,59 @@
+<script lang="ts">
+  import { snap } from "../stores/snapshot.svelte";
+  import { formatDifficulty } from "../format";
+
+  // Top 10 workers by all-time best share. `bestever` requires the
+  // Kamado ckpool patch (0001-expose-bestever-in-runtime-json.patch)
+  // — on an unpatched ckpool it will be zero everywhere and we fall
+  // back to the current round's best diff.
+  const rows = $derived.by(() => {
+    const ws = snap.data?.workers ?? [];
+    const enriched = ws.map((w) => ({
+      worker: w.worker,
+      bestRound: w.bestdiff,
+      bestEver: w.bestever || w.bestdiff,
+    }));
+    enriched.sort((a, b) => b.bestEver - a.bestEver);
+    return enriched.slice(0, 10);
+  });
+</script>
+
+<section class="card">
+  <h2>Best shares leaderboard</h2>
+  {#if rows.length === 0}
+    <div class="empty">No shares submitted yet.</div>
+  {:else}
+    <table>
+      <thead>
+        <tr>
+          <th>#</th>
+          <th>Worker</th>
+          <th class="num">Best (round)</th>
+          <th class="num">Best (ever)</th>
+        </tr>
+      </thead>
+      <tbody>
+        {#each rows as r, i (r.worker)}
+          <tr>
+            <td>{i + 1}</td>
+            <td class="mono">{r.worker}</td>
+            <td class="num">{formatDifficulty(r.bestRound)}</td>
+            <td class="num">{formatDifficulty(r.bestEver)}</td>
+          </tr>
+        {/each}
+      </tbody>
+    </table>
+  {/if}
+</section>
+
+<style>
+  h2 {
+    margin: 0 0 1rem;
+    font-size: 1.05rem;
+    font-weight: 600;
+  }
+  .empty {
+    color: var(--fg-dim);
+    padding: 0.5rem 0;
+  }
+</style>