feat(web): score an already-annotated case without re-running the pipeline

A case analysed before a model existed stayed unscored forever: the only control on the page
was "Re-analyse case", which re-runs five minutes of VEP to obtain a score that takes a second.
When any candidate is unscored the page now offers "Score variants" on its own.

Tests: web 34; svelte-check clean.

web/src/routes/cases/[id]/+page.svelte

@@ -3,7 +3,7 @@
   import { api, type Candidate, type CandidatePage, type Case, type Job, type VariantDetail } from '$lib/api';
   import { poll } from '$lib/poll';
   import { formatElapsed, latestStep } from '$lib/progress';
-  import { plural } from '$lib/candidates';
+  import { needsScoring, plural } from '$lib/candidates';
   import CandidateRow from '$lib/components/CandidateRow.svelte';
   import Funnel from '$lib/components/Funnel.svelte';
   import VariantPanel from '$lib/components/VariantPanel.svelte';
@@ -31,6 +31,9 @@
   const elapsedMs = $derived(job ? now - Date.parse(job.created_at) : 0);
   const step = $derived(scoring ? 'scoring variants with the model' : latestStep(job?.log ?? null));
   const termCount = $derived(kase?.phenotypes.length ?? 0);
+  // Annotation is expensive and scoring is not: a case annotated before a model existed should
+  // not need a five-minute re-run of VEP to get its score.
+  const unscored = $derived(!!page && page.items.length > 0 && needsScoring(page.items));
 
   // Tick the elapsed time while a run is in flight; polling refreshes the step itself.
   $effect(() => {
@@ -154,6 +157,9 @@
 {:else}
   <p class="actions">
     <button onclick={analyse} disabled={busy}>{job ? 'Re-analyse case' : 'Analyse case'}</button>
+    {#if unscored}
+      <button class="quiet" onclick={scoreThenLoad}>Score variants</button>
+    {/if}
     {#if page && page.funnel.total > 0}
       <a class="reportlink" href="/cases/{data.caseId}/report">Case report →</a>
     {/if}