docs: add a cross-language examples index

The top-level examples/ directory held only python/, which made the
examples look Python-only even though Rust, Node and WASM all ship their
own. Add examples/README.md: a single index of every runnable example
across Rust, Python, Node and WASM, each with its run command, plus a note
on the bundled BTCUSDT datasets.

Point the README "Languages" table at the Node backtest example and link
the new index from both the table and the project-layout section.

README.md

@@ -118,10 +118,13 @@ 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/streaming.js` |
+| Node.js (napi-rs) | `npm install wickra`                          | `bindings/node/examples/backtest.js` |
 | Browser / WASM    | `npm install wickra-wasm`                     | `bindings/wasm/examples/index.html` |
 | Rust              | `cargo add wickra`                            | `crates/wickra/examples/backtest.rs` |
 
+Each binding ships several runnable examples (streaming, backtest, live feed);
+[`examples/README.md`](examples/README.md) is the full cross-language index.
+
 The wickra-core crate is `unsafe`-forbidden, so every binding inherits a
 memory-safe implementation.
 
@@ -188,7 +191,7 @@ wickra/
 │   ├── python/              PyO3 + maturin (publishes on PyPI)
 │   ├── node/                napi-rs (publishes on npm) + examples/
 │   └── wasm/                wasm-bindgen (browsers, bundlers, Node) + examples/
-├── examples/
+├── examples/                examples/README.md indexes every language
 │   └── python/              backtest, live trading, parallel assets, multi-tf
 └── .github/workflows/       CI and release pipelines
 ```