examples: migrate to the native data layer (drop ws/coder-websocket/jackson/jsonlite) (#316)

Stacked on #315 (the native Binance REST fetcher). Retarget to `main` once #315 merges.

Migrates the runnable examples off third-party data-I/O packages onto Wickra's
native data layer (`CandleReader`, `Resampler`, `BinanceFeed`, `fetch_*klines`).

## Third-party packages removed (the zero-dep selling point)
- **Node**: `ws` (live feed → BinanceFeed) — dropped from package.json + lockfile
- **Go**: `github.com/coder/websocket` — dropped from go.mod / go.sum (`go mod tidy`)
- **Java**: `jackson-databind` (live feed + REST fetch) — dropped from pom.xml
- **R**: `jsonlite` + `websocket` + `later` — dropped from the README notes

Each language's CSV loading now goes through `CandleReader`, manual resampling
through `Resampler`, the live feed through `BinanceFeed`, and (Java/R) the REST
download through the native fetcher.

## Verification
Ran the offline examples per language against the bundled data — backtest and
multi_timeframe produce identical output across Python / Node / Go / Java / R
(e.g. ATR(14) last 345.1010; 1h→5m resamples to 240 bars, →15m to 80 bars).

C# / C / WASM (stdlib-only, no third-party deps to remove) follow in this branch.

Note: the streaming `strategy_*` examples have pre-existing candle-indicator
runtime bugs (CI only syntax-smokes them); the CSV migration preserves their
shape and leaves those bugs for a separate fix.

examples/node/strategy_bollinger_squeeze.js

@@ -31,48 +31,14 @@ const ATR_PERIOD = 14;
 const ATR_STOP_MULT = 2.0;
 const SQUEEZE_LOOKBACK = 180;
 
-const REQUIRED_COLUMNS = ['timestamp', 'open', 'high', 'low', 'close', 'volume'];
 const DEFAULT_CSV = path.join(__dirname, '..', 'data', 'btcusdt-1d.csv');
 
 function loadCandles(csvPath) {
+  // Native CandleReader: validates the header, tolerates a UTF-8 BOM and field
+  // whitespace, and throws on a malformed row. Yields { open, high, low, close,
+  // volume, timestamp } objects.
   const text = fs.readFileSync(csvPath, 'utf8');
-  const lines = text.split(/\r?\n/).filter((line) => line.length > 0);
-  if (lines.length === 0) {
-    throw new Error(`${csvPath}: file is empty`);
-  }
-
-  const header = lines[0].split(',').map((cell) => cell.trim());
-  const missing = REQUIRED_COLUMNS.filter((col) => !header.includes(col));
-  if (missing.length > 0) {
-    throw new Error(
-      `${csvPath}: CSV header is missing required column(s): ${missing.join(', ')}; ` +
-        `found: ${header.join(', ')}`,
-    );
-  }
-  if (lines.length === 1) {
-    throw new Error(`${csvPath}: CSV has a header but no data rows`);
-  }
-
-  const idx = {};
-  for (const col of REQUIRED_COLUMNS) idx[col] = header.indexOf(col);
-
-  const candles = [];
-  for (let row = 1; row < lines.length; row++) {
-    const cells = lines[row].split(',');
-    const candle = {};
-    for (const col of ['open', 'high', 'low', 'close', 'volume']) {
-      const raw = cells[idx[col]];
-      const value = raw === undefined ? NaN : Number(raw.trim());
-      if (raw === undefined || raw.trim() === '' || !Number.isFinite(value)) {
-        throw new Error(
-          `${csvPath}: row ${row + 1} column '${col}' is not numeric: ${JSON.stringify(raw)}`,
-        );
-      }
-      candle[col] = value;
-    }
-    candles.push(candle);
-  }
-  return candles;
+  return new wickra.CandleReader(text).read();
 }
 
 function signed(value, digits) {