Fix run detail: default to JSON, only HTML if browser requests it

API clients like Python requests send Accept: */* which wasn't
matching wants_json(). Switch to checking wants_html() instead
so API clients get JSON by default.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/routers/runs.py

@@ -100,15 +100,16 @@ async def get_run(
     if not run:
         raise HTTPException(404, f"Run {run_id} not found")
 
-    if wants_json(request):
-        return run
+    # Only render HTML if browser explicitly requests it
+    if wants_html(request):
+        templates = get_templates(request)
+        return render(templates, "runs/detail.html", request,
+            run=run,
+            active_tab="runs",
+        )
 
-    # Render HTML detail page
-    templates = get_templates(request)
-    return render(templates, "runs/detail.html", request,
-        run=run,
-        active_tab="runs",
-    )
+    # Default to JSON for API clients
+    return run
 
 
 @router.delete("/{run_id}")