feat(atlas): Phase C — recent-runs timeline

A strip of the last 12 runs (aggregate pass/fail/running per run) below the
substrate ribbon, coloured, newest-first, run # on hover. Parsed from the same
Gitea /actions/tasks fetch (RecentRuns, test-first; State refactored to share
the aggregate). No new RBAC. Hidden when no live data.

Verified: build/vet/lint(0)/test green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/atlas/runs_test.go

@@ -65,6 +65,30 @@ func TestRunNodes_SummaryThenPerJobColoured(t *testing.T) {
 	}
 }
 
+func TestRecentRuns_GroupsRunsNewestFirstWithAggregateState(t *testing.T) {
+	tasks := []byte(`{"workflow_runs":[
+	  {"run_number":28,"name":"Deploy","status":"success"},
+	  {"run_number":28,"name":"Build","status":"success"},
+	  {"run_number":27,"name":"Deploy","status":"completed","conclusion":"failure"},
+	  {"run_number":26,"name":"Build","status":"running"},
+	  {"run_number":25,"name":"Deploy","status":"success"}
+	]}`)
+
+	dots, err := atlas.RecentRuns(tasks, 3)
+	if err != nil {
+		t.Fatalf("RecentRuns: %v", err)
+	}
+	if len(dots) != 3 {
+		t.Fatalf("want 3 dots (capped), got %d: %+v", len(dots), dots)
+	}
+	want := []atlas.RunDot{{28, "success"}, {27, "failure"}, {26, "running"}}
+	for i := range want {
+		if dots[i] != want[i] {
+			t.Fatalf("dot[%d] = %+v, want %+v", i, dots[i], want[i])
+		}
+	}
+}
+
 func TestLatestRunJobs_ErrorsWhenEmpty(t *testing.T) {
 	if _, err := atlas.LatestRunJobs([]byte(`{"workflow_runs":[]}`)); err == nil {
 		t.Fatal("expected error on empty, got nil")