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>

README.md

@@ -93,16 +93,19 @@ The home page can store the API key in `sessionStorage` when you are not using c
 ## Layout
 
 - `src/` — FastAPI app and static UI (`src/static/`)
-- `workspace/` — default tree: `code/` (editable), `lib/` (read-only via API)
+- `lib/` — bundled MicroPython stubs (copied into `WORKSPACE_ROOT/lib` when missing; read-only via API)
+- `workspace/` — default `WORKSPACE_ROOT`: `code/` samples (editable); runtime `lib/` is filled from `lib/` above
 
 ## ESP32 / NeoPixel mock
 
-The browser runtime now includes MicroPython-style mocks in `workspace/lib`:
+The browser runtime ships MicroPython-style stubs in repo `lib/` (they appear as `lib/` in the editor and are read-only via the APIs):
 
-- `machine.Pin`
+- `machine.Pin`, `machine.freq()`, `machine.unique_id()`, `machine.reset()` (no-op here)
 - `neopixel.NeoPixel`
+- `utime` — `ticks_ms`, `ticks_diff`, `ticks_add`, `sleep_ms`, `sleep_us`, `sleep`
+- `micropython.const` — no-op helper for ported constant declarations
 
-Use them from scripts in `workspace/code` exactly like ESP32 examples:
+Use them from scripts in `workspace/code` like typical ESP32 / MicroPython examples:
 
 ```python
 from machine import Pin