feat(ui): show merged-into-parent badge on adopted observations

ObservationCard renders a secondary "merged → <parent>" chip when
merged_into_project is set, next to the existing project label.
Both are meaningful: project is origin provenance, merged_into_project
is the current home.

Extends PaginationHelper's observations and summaries queries with
OR merged_into_project = ? so the single-project viewer fetch pulls
in adopted rows — the plan's Phase 3 covered multi-project context
injection; this is the single-project UI read path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ui/viewer-template.html

@@ -1130,6 +1130,19 @@
       color: var(--color-text-muted);
     }
 
+    /* Merged-into-parent provenance badge */
+    .card-merged-badge {
+      padding: 1px 6px;
+      border-radius: 3px;
+      font-size: 9px;
+      font-weight: 500;
+      letter-spacing: 0.02em;
+      color: var(--color-text-muted);
+      background: var(--color-type-badge-bg);
+      border: 1px solid var(--color-border);
+      opacity: 0.85;
+    }
+
     .summary-card {
       border-color: var(--color-border-summary);
       background: var(--color-bg-summary);