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.

examples/node/streaming.js

@@ -0,0 +1,77 @@
+// Streaming indicators with the Wickra Node binding.
+//
+// Feeds a synthetic price series through several indicators tick by tick —
+// the same O(1)-per-update model a live trading bot would use — and prints a
+// status line whenever every indicator has warmed up.
+//
+// Run it from the repository after building the native binding:
+//
+//   cd bindings/node && npm install && npx napi build --platform --release
+//   cd ../../examples/node && npm install
+//   node streaming.js
+
+const wickra = require('wickra');
+
+// A deterministic synthetic series: a slow trend with two oscillations and a
+// little noise from a seeded generator (so every run prints the same thing).
+function makeSeries(n) {
+  let seed = 1234567;
+  const rand = () => {
+    seed = (seed * 1103515245 + 12345) & 0x7fffffff;
+    return seed / 0x7fffffff;
+  };
+  const prices = [];
+  for (let t = 0; t < n; t++) {
+    const price =
+      100 +
+      t * 0.05 +
+      Math.sin(t * 0.07) * 8 +
+      Math.cos(t * 0.21) * 3 +
+      (rand() - 0.5);
+    prices.push(price);
+  }
+  return prices;
+}
+
+const fmt = (v) =>
+  v === null || v === undefined || Number.isNaN(v) ? '  --  ' : v.toFixed(2);
+
+function main() {
+  console.log(`Wickra ${wickra.version()} — streaming indicator demo\n`);
+
+  const sma = new wickra.SMA(20);
+  const ema = new wickra.EMA(20);
+  const rsi = new wickra.RSI(14);
+  const macd = new wickra.MACD(12, 26, 9);
+
+  const prices = makeSeries(120);
+  let signals = 0;
+
+  for (let t = 0; t < prices.length; t++) {
+    const price = prices[t];
+    const smaV = sma.update(price);
+    const emaV = ema.update(price);
+    const rsiV = rsi.update(price);
+    const macdV = macd.update(price); // { macd, signal, histogram } or null
+
+    // Only act once every indicator has produced a value.
+    if (smaV == null || emaV == null || rsiV == null || macdV == null) {
+      continue;
+    }
+
+    const overbought = rsiV > 70 && macdV.histogram < 0;
+    const oversold = rsiV < 30 && macdV.histogram > 0;
+    const tag = overbought ? 'SELL?' : oversold ? 'BUY? ' : '     ';
+    if (overbought || oversold) signals++;
+
+    console.log(
+      `t=${String(t).padStart(3)}  price=${fmt(price)}  ` +
+        `sma=${fmt(smaV)}  ema=${fmt(emaV)}  rsi=${fmt(rsiV)}  ` +
+        `macd_hist=${fmt(macdV.histogram)}  ${tag}`,
+    );
+  }
+
+  console.log(`\nDone — ${signals} candidate signal(s) over ${prices.length} ticks.`);
+}
+
+main();