Record and display winning share difficulty on found blocks

Logmon now captures the share diff from ckpool's "Possible block
solve" line preceding the confirmation and attaches it to the
BlockEvent. Persisted as share_diff alongside height/hash/reward
and rendered as a new column in the dashboard block history.

ui/src/lib/BlocksTable.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
   import { snap } from "../stores/snapshot.svelte";
-  import { formatAgo } from "../format";
+  import { formatAgo, formatDifficulty } from "../format";
 
   const blocks = $derived.by(() => {
     const b = snap.data?.recent_blocks ?? [];
@@ -12,18 +12,16 @@
 <section class="card">
   <h2>Blocks found</h2>
   {#if blocks.length === 0}
-    <div class="empty">
-      No blocks found yet. Any solve will appear here instantly via the
-      log tailer, and persist to SQLite once Phase 2b.5 ships.
-    </div>
+    <div class="empty">No blocks found yet.</div>
   {:else}
     <table>
       <thead>
         <tr>
           <th>Height</th>
           <th>Hash</th>
+          <th class="num">Reward</th>
+          <th class="num">Winning share</th>
           <th class="num">When</th>
-          <th>Source</th>
         </tr>
       </thead>
       <tbody>
@@ -31,8 +29,9 @@
           <tr>
             <td class="mono">{b.height}</td>
             <td class="hash mono">{b.hash ? b.hash.slice(0, 16) + "…" : "—"}</td>
+            <td class="num">{b.reward_btc ? b.reward_btc.toFixed(4) + " BTC" : "—"}</td>
+            <td class="num">{b.share_diff ? formatDifficulty(b.share_diff) : "—"}</td>
             <td class="num">{formatAgo(new Date(b.found_at).getTime() / 1000)}</td>
-            <td>{b.source}</td>
           </tr>
         {/each}
       </tbody>