Ship MicroPython stubs from repo lib/ and seed workspace lib on startup

Move machine.py and neopixel.py into a tracked /lib/ at the repo root and
auto-copy them into WORKSPACE_ROOT/lib whenever files are missing, so empty
volumes and fresh per-user workspaces always have the read-only stubs
available to Jedi and Pyodide. Allow all users to browse lib/ in the UI
(writes still gated by the API), and add tests covering initial seeding
and re-population after the dir is wiped.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_internal.py

@@ -43,3 +43,4 @@ def test_collect_python_sources_skips_hidden_and_binary(tmp_path):
     out = filesystem.collect_python_sources()
     assert out["code/ok.py"] == "a = 1\n"
     assert "bad.py" not in out
+    assert "lib/machine.py" in out, "shared lib stubs should always be merged for Jedi / Pyodide"