fix(dashboard): remove Lineage commit associations from Task Changes UI

The lineage commit associations panel surfaced low-value provenance
metadata. Remove the UI section, its dead state/fetch wiring in
TaskChangesTab, the orphaned .task-lineage-* CSS, and the obsolete
tests. The fetchTaskCommitAssociations API helper is retained.

packages/dashboard/app/components/TaskChangesTab.css

@@ -35,103 +35,3 @@
   box-shadow: none;
 }
 
-.task-lineage-associations {
-  display: flex;
-  flex-direction: column;
-  gap: var(--space-sm);
-  margin-bottom: var(--space-md);
-  padding: var(--space-sm);
-  border: 1px solid var(--border);
-  border-radius: var(--radius-md);
-  background: var(--surface);
-}
-
-.task-lineage-associations-header {
-  display: flex;
-  align-items: center;
-  justify-content: space-between;
-  gap: var(--space-sm);
-}
-
-.task-lineage-associations-header h4 {
-  display: inline-flex;
-  align-items: center;
-  gap: var(--space-xs);
-  margin: 0;
-}
-
-.task-lineage-id,
-.task-lineage-sha {
-  font-family: var(--font-mono);
-  font-size: 0.75rem;
-}
-
-.task-lineage-associations-empty {
-  margin: 0;
-  color: var(--text-muted);
-}
-
-.task-lineage-associations-list {
-  display: flex;
-  flex-direction: column;
-  gap: var(--space-xs);
-}
-
-.task-lineage-association {
-  display: flex;
-  flex-direction: column;
-  gap: var(--space-xs);
-  padding: var(--space-sm);
-  border-radius: var(--radius-sm);
-  border: 1px solid var(--border);
-  background: var(--card);
-}
-
-.task-lineage-association--legacy,
-.task-lineage-association--ambiguous {
-  opacity: 0.78;
-}
-
-.task-lineage-association-main {
-  display: flex;
-  align-items: center;
-  gap: var(--space-sm);
-}
-
-.task-lineage-subject {
-  min-width: 0;
-  overflow: hidden;
-  text-overflow: ellipsis;
-  white-space: nowrap;
-}
-
-.task-lineage-association-meta {
-  display: flex;
-  flex-wrap: wrap;
-  gap: var(--space-sm);
-  color: var(--text-muted);
-  font-size: 0.75rem;
-}
-
-.task-lineage-note {
-  margin: 0;
-  color: var(--text-dim);
-  font-size: 0.75rem;
-}
-
-@media (max-width: 768px) {
-  .task-lineage-associations-header {
-    flex-direction: column;
-    align-items: flex-start;
-  }
-
-  .task-lineage-association-main {
-    flex-wrap: wrap;
-  }
-
-  .task-lineage-subject {
-    white-space: normal;
-    overflow: visible;
-    text-overflow: clip;
-  }
-}