examples: move Node examples into a top-level examples/node/

Continue the per-language `examples/<lang>/` restructure: move the three
Node example files (streaming.js, backtest.js, live_trading.js) out of
bindings/node/examples/ and into a top-level examples/node/ directory.

* `examples/node/package.json` is a `private` package that pulls the
  native binding via `file:../../bindings/node` and lists `ws` as a
  dev-dependency for the live-trading example. `require('..')` in each
  file becomes `require('wickra')` — exactly what a downstream user would
  write — and the file-header run instructions are updated to the new
  two-step workflow (`npm install` in bindings/node, then in
  examples/node).
* `backtest.js`'s default-CSV path becomes the much shorter
  `__dirname/../data/btcusdt-1d.csv` from the new location.
* `bindings/node/package.json` drops the now-unused `ws` devDependency.
* `.gitignore` is broadened from `bindings/node/node_modules/` to
  `**/node_modules/` so the new `examples/node/node_modules/` directory is
  not tracked.
* The README "Languages" table, project-layout block and
  `examples/README.md` Node section are updated for the new paths and run
  commands.

Verified by running `node backtest.js` (3200 BTCUSDT daily bars, matching
output), `node streaming.js`, and `node --check live_trading.js` from the
new location.

README.md

@@ -118,7 +118,7 @@ inherit it automatically.
 | Binding           | Install                                       | Example |
 |-------------------|-----------------------------------------------|---------|
 | Python (PyO3)     | `pip install wickra`                          | `examples/python/backtest.py` |
-| Node.js (napi-rs) | `npm install wickra`                          | `bindings/node/examples/backtest.js` |
+| Node.js (napi-rs) | `npm install wickra`                          | `examples/node/backtest.js` |
 | Browser / WASM    | `npm install wickra-wasm`                     | `bindings/wasm/examples/index.html` |
 | Rust              | `cargo add wickra`                            | `examples/rust/src/bin/backtest.rs` |
 
@@ -186,12 +186,13 @@ wickra/
 │   └── wickra-data/         CSV reader, tick aggregator, live exchange feeds
 ├── bindings/
 │   ├── python/              PyO3 + maturin (publishes on PyPI)
-│   ├── node/                napi-rs (publishes on npm) + examples/
+│   ├── node/                napi-rs (publishes on npm)
 │   └── wasm/                wasm-bindgen (browsers, bundlers, Node) + examples/
 ├── examples/                examples/README.md indexes every language
 │   ├── data/                real BTCUSDT OHLCV datasets, one per timeframe
 │   ├── rust/                Rust workspace member (`wickra-examples`)
-│   └── python/              backtest, live trading, parallel assets, multi-tf
+│   ├── python/              backtest, live trading, parallel assets, multi-tf
+│   └── node/                streaming, backtest, live trading (load `wickra`)
 └── .github/workflows/       CI and release pipelines
 ```