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/PoolOverview.svelte

@@ -0,0 +1,58 @@
+<script lang="ts">
+  import { snap } from "../stores/snapshot.svelte";
+  import {
+    formatHashrate,
+    formatUptime,
+    expectedBlockSeconds,
+    formatDuration,
+  } from "../format";
+
+  const data = $derived(snap.data!);
+  const miners = $derived(data.clients?.length ?? 0);
+  const workerCount = $derived(data.workers?.length ?? 0);
+
+  // Pool share of the network hashrate, used both for display and for
+  // the expected-block calculation. Network diff comes from bitcoind.
+  const poolShare = $derived.by(() => {
+    const net = data.network_hashrate_hs;
+    if (!net || net <= 0) return 0;
+    return data.hashrate_hs_1h / net;
+  });
+
+  const expected = $derived.by(() => {
+    const diff = data.chain?.difficulty ?? 0;
+    return expectedBlockSeconds(data.hashrate_hs_1h, data.network_hashrate_hs, diff);
+  });
+</script>
+
+<section class="grid grid-4">
+  <div class="card">
+    <div class="stat-label">Hashrate (1h)</div>
+    <div class="stat-value">{formatHashrate(data.hashrate_hs_1h)}</div>
+    <div class="stat-sub">
+      1m {formatHashrate(data.hashrate_hs_1m)} · 5m {formatHashrate(data.hashrate_hs_5m)}
+      · 24h {formatHashrate(data.hashrate_hs_24h)}
+    </div>
+  </div>
+
+  <div class="card">
+    <div class="stat-label">Miners</div>
+    <div class="stat-value">{miners}</div>
+    <div class="stat-sub">{workerCount} workers · {data.users?.length ?? 0} users</div>
+  </div>
+
+  <div class="card">
+    <div class="stat-label">Network</div>
+    <div class="stat-value">{formatHashrate(data.network_hashrate_hs)}</div>
+    <div class="stat-sub">
+      diff {data.chain?.difficulty.toExponential(2) ?? "—"} ·
+      share {(poolShare * 1e9).toFixed(2)} ppb
+    </div>
+  </div>
+
+  <div class="card">
+    <div class="stat-label">Expected block</div>
+    <div class="stat-value">{formatDuration(expected)}</div>
+    <div class="stat-sub">uptime {formatUptime(data.uptime_seconds)}</div>
+  </div>
+</section>