fix(labs/lab_05): import plotly.subplots AFTER micropip install

pre-existing bug caught by loading the dev preview in a real browser.

the setup cell imported `from plotly.subplots import make_subplots` at line 55, BEFORE the `await micropip.install([..., "plotly", ...])` at line 60. in WASM (emscripten), plotly isn't available at import time — it's installed at runtime via micropip. the top-level import fails with ModuleNotFoundError, and every downstream cell that depends on the setup cell cascades with "ancestor raised".

fix: move the plotly.subplots import to after the micropip install block, alongside `import plotly.graph_objects as go` which was already in the right place.

caught only by manual browser verification on the dev preview site. the existing CI checks (marimo check, test_engine in native python, WASM smoke test byte-size check) all passed because they don't actually run the exported HTML in a browser.

labs/vol2/lab_05_dist_train.py

@@ -52,7 +52,6 @@ async def _():
     import math
     from pathlib import Path
     import numpy as np
-    from plotly.subplots import make_subplots
 
     # WASM bootstrap
     if sys.platform == "emscripten":
@@ -66,6 +65,8 @@ async def _():
         if str(_root) not in sys.path:
             sys.path.insert(0, str(_root))
 
+    # plotly must be imported AFTER micropip install, since it's installed at runtime on WASM
+    from plotly.subplots import make_subplots
     import plotly.graph_objects as go
     from mlsysim.labs.state import DesignLedger
     from mlsysim.labs.style import COLORS, LAB_CSS, apply_plotly_theme