feat(evidence): record provenance and stop derived evidence counting as corroboration

Every evidence row now records its derivation (direct, assertion, operator,
external, prediction, consolidation, inference, reflection, dream,
retrieval), its independent-source family (an actor, an integration, an
operator, a prediction) and its root event or memory ids. Confidence
groups evidence by family: the strongest primary item counts in full, each
further primary item adds a quarter, capped at 1.5x, and derived items
count only when the family has no primary member. Three derived
re-expressions of one utterance therefore weigh exactly what the utterance
weighs, while three independent families still add up.

Producers (conversation, association, consolidation, predictions,
metacognition, dreaming, operator and seed input, contradictions) supply
their ancestry. Existing rows are marked legacy_unknown with family =
source; nothing is invented. The belief page shows per-family
contributions and the replay test checks that provenance is reconstructed
identically in the sandbox. Migration 0017 is additive.

web/templates/pages/belief_detail.html

@@ -22,7 +22,8 @@
     <div class="grid cols-2">
       <div class="card">
         <h2>Evidence for</h2>
-        <ul class="plain ev">{{range $d.Evidence}}{{if eq .Direction "for"}}<li class="{{if .Retracted}}retracted{{end}}"><div><strong>{{conf .Weight}}</strong> × cred {{conf .Credibility}} <span class="badge">{{.Kind}}</span> {{if .Retracted}}<span class="badge danger">retracted</span>{{end}}</div><div>{{.Note}}</div><div class="muted small">{{.Source}} · {{ago .CreatedAt}} {{if and (eq .Kind "event") .RefID}}· <a href="/events/{{.RefID}}">event</a>{{else if and (eq .Kind "memory") .RefID}}· <a href="/minds/{{$m.Slug}}/memory/{{.RefID}}">memory</a>{{else if and (eq .Kind "belief") .RefID}}· <a href="/minds/{{$m.Slug}}/beliefs/{{.RefID}}">belief</a>{{end}}</div></li>{{end}}{{else}}<li class="muted">None.</li>{{end}}</ul>
+        <ul class="plain ev">{{range $d.Evidence}}{{if eq .Direction "for"}}<li class="{{if .Retracted}}retracted{{end}}"><div><strong>{{conf .Weight}}</strong> × cred {{conf .Credibility}} <span class="badge">{{.Kind}}</span> {{if .Retracted}}<span class="badge danger">retracted</span>{{end}}</div><div>{{.Note}}</div><div class="muted small">{{.Source}} · {{ago .CreatedAt}} {{if and (eq .Kind "event") .RefID}}· <a href="/events/{{.RefID}}">event</a>{{else if and (eq .Kind "memory") .RefID}}· <a href="/minds/{{$m.Slug}}/memory/{{.RefID}}">memory</a>{{else if and (eq .Kind "belief") .RefID}}· <a href="/minds/{{$m.Slug}}/beliefs/{{.RefID}}">belief</a>{{end}}</div><div class="muted small">provenance: <span class="badge small">{{.Derivation}}</span> family <code>{{.Family}}</code>{{if eq .ProvenanceStatus "legacy_unknown"}} <span class="badge warn small" title="written before ancestry was recorded; family is the source string">legacy</span>{{end}}{{range .RootIDs}} · <a href="/events/{{.}}">root</a>{{end}}</div></li>{{end}}{{else}}<li class="muted">None.</li>{{end}}</ul>
+        {{if $bd.Families}}<h3 class="small muted">Independent sources</h3><table class="table compact"><thead><tr><th>Family</th><th></th><th class="num">Items</th><th class="num">Primary</th><th class="num">Counts as</th></tr></thead><tbody>{{range $bd.Families}}<tr><td><code>{{.Family}}</code></td><td class="small">{{.Direction}}</td><td class="num">{{.Items}}</td><td class="num">{{.Primary}}</td><td class="num">{{printf "%.2f" .Contribution}}</td></tr>{{end}}</tbody></table><p class="small muted">Within a family the strongest primary item counts in full and further items add a quarter each (capped at 1.5×); derived items count only when the family has no primary item. Diversity counts families: {{$bd.SourcesFor}}.</p>{{end}}
       </div>
       <div class="card">
         <h2>Evidence against</h2>