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/App.svelte

@@ -0,0 +1,51 @@
+<script lang="ts">
+  import { onMount } from "svelte";
+  import { connect, snap } from "./stores/snapshot.svelte";
+  import Header from "./lib/Header.svelte";
+  import PoolOverview from "./lib/PoolOverview.svelte";
+  import MinersTable from "./lib/MinersTable.svelte";
+  import BlocksTable from "./lib/BlocksTable.svelte";
+  import BestShares from "./lib/BestShares.svelte";
+
+  onMount(() => {
+    connect();
+  });
+</script>
+
+<main>
+  <Header />
+
+  {#if !snap.data}
+    <div class="card placeholder">
+      <div class="stat-label">Status</div>
+      <div class="stat-value">Connecting to kamado-api…</div>
+      {#if snap.error}
+        <div class="stat-sub bad">{snap.error}</div>
+      {/if}
+    </div>
+  {:else}
+    <PoolOverview />
+    <div class="grid grid-2">
+      <BlocksTable />
+      <BestShares />
+    </div>
+    <MinersTable />
+  {/if}
+</main>
+
+<style>
+  main {
+    max-width: 1280px;
+    margin: 0 auto;
+    padding: 1.5rem 1.25rem 4rem;
+    display: flex;
+    flex-direction: column;
+    gap: 1.25rem;
+  }
+  .placeholder {
+    text-align: center;
+  }
+  .bad {
+    color: var(--bad);
+  }
+</style>