feat(beliefs): state what a score means; gated calibration; primary uncertainty

Every breakdown now carries its meaning: an uncalibrated epistemic score
derived from recorded evidence, not a probability of truth. Belief detail
adds a calibrated estimate read from the mind's resolved predictions when
at least twenty were decided in the score's range, and otherwise says why
none is shown; and names the primary uncertainty deterministically (no live
evidence, conflicting evidence, second-hand only, unclear reading, a single
source family, little evidence). The belief list heading becomes Score.

web/templates/pages/belief_detail.html

@@ -3,6 +3,9 @@
 <div class="pagehead">
   <p class="muted small"><a href="/minds/{{$m.Slug}}">{{$m.DisplayName}}</a> › <a href="/minds/{{$m.Slug}}/beliefs">beliefs</a></p>
   <h1><span class="badge st-{{$b.Status}}">{{$b.Status}}</span> {{$b.Proposition}}</h1>
+  <p class="score-line"><strong>Epistemic score {{conf $b.Confidence}}</strong> <span class="muted small">(uncalibrated: derived from recorded evidence, not a probability of truth)</span>
+    · calibrated: {{if $d.Calibration.Available}}<strong>{{conf $d.Calibration.Estimate}}</strong> <span class="muted small">(hit rate of {{$d.Calibration.SampleSize}} decided predictions in this range)</span>{{else}}<span class="muted small">not available ({{$d.Calibration.Reason}})</span>{{end}}
+    · main uncertainty: <span class="muted">{{$d.PrimaryUncertainty}}</span></p>
   <p class="muted">{{$b.Epistemic}} · version {{$b.Version}} · first {{date $b.FirstCreated}} · evaluated {{$b.Evaluations}}× · source {{$b.Source}}{{if $b.Subject}} · subject <span class="mono">{{$b.Subject}}</span>{{end}}{{if $b.PinnedStatus}} · <span class="badge warn">status pinned by operator</span>{{end}}</p>
 </div>
 <section class="grid cols-3-1">

web/templates/pages/beliefs.html

@@ -15,7 +15,7 @@
   <div class="card">
     {{if .Data.Beliefs}}
     <table class="table compact">
-      <thead><tr><th>Status</th><th>Proposition</th><th class="num">Confidence</th><th>Kind</th><th>Evaluated</th></tr></thead>
+      <thead><tr><th>Status</th><th>Proposition</th><th class="num" title="uncalibrated epistemic score derived from evidence; not a probability of truth">Score</th><th>Kind</th><th>Evaluated</th></tr></thead>
       <tbody>{{range .Data.Beliefs}}<tr>
         <td><span class="badge st-{{.Status}}">{{.Status}}</span></td>
         <td><a href="/minds/{{$m.Slug}}/beliefs/{{.ID}}">{{.Proposition}}</a>{{if .Subject}} <span class="muted small mono">{{.Subject}}</span>{{end}}</td>