feat(microstructure): trade-sign autocorrelation, PIN, Hasbrouck information share (B15) (#212)

## B15 Microstructure — three new indicators (485 → 488)

| Indicator | Input | Output | Notes |
|-----------|-------|--------|-------|
| `TradeSignAutocorrelation` | `Trade` | `f64` ∈ [-1,1] | lag-1 autocorrelation of the signed aggressor (order-flow persistence) |
| `Pin` | `Trade` | `f64` ∈ [0,1] | probability of informed trading from rolling buy/sell imbalance (EKOP single-window estimator); `name()` = `"PIN"` |
| `HasbrouckInformationShare` | `(f64, f64)` | `f64` ∈ [0,1] | variance-ratio proxy for each venue's share of price discovery |

### Wiring
- Core structs + full unit tests (every branch).
- Hand-written Python/Node/WASM bindings for the two `Trade`-input indicators (precedent `TradeImbalance`); `node_pair_indicator!` / `wasm_pair_indicator!` macro bindings + hand Python pyclass for the pairwise Hasbrouck (precedent `RollingCorrelation`).
- Fuzz drives added to `indicator_update_trade.rs` and `indicator_update_pair.rs`.
- Dedicated Python + Node streaming-vs-batch and reference tests; Hasbrouck in the `PAIR` registry.
- README counter (3 spots) + `docs/README.md` + `FAMILIES` assert bumped to 488.

### Verify (all green, local)
- `cargo test -p wickra-core --lib`: 3991 passed
- `cargo test -p wickra-core --doc`: 438 passed
- `cargo clippy --workspace --all-targets --all-features -- -D warnings`: clean
- node: 561 passed · pytest: 926 passed

bindings/node/__tests__/indicators.test.js

@@ -667,6 +667,7 @@ const pairFactories = {
   GrangerCausality: () => new wickra.GrangerCausality(60, 1),
   SpreadAr1Coefficient: () => new wickra.SpreadAr1Coefficient(40),
   KendallTau: () => new wickra.KendallTau(20),
+  HasbrouckInformationShare: () => new wickra.HasbrouckInformationShare(2),
 };
 
 for (const [name, make] of Object.entries(pairFactories)) {
@@ -1270,7 +1271,7 @@ test('vpin / amihud / roll reference + streaming matches batch', () => {
   const price = Array.from({ length: n }, (_, i) => 100 + Math.sin(i * 0.25) * 4);
   const size = Array.from({ length: n }, (_, i) => 1 + (i % 5));
   const isBuy = Array.from({ length: n }, (_, i) => i % 2 === 0);
-  for (const make of [() => new wickra.Vpin(8, 5), () => new wickra.AmihudIlliquidity(14), () => new wickra.RollMeasure(14)]) {
+  for (const make of [() => new wickra.Vpin(8, 5), () => new wickra.AmihudIlliquidity(14), () => new wickra.RollMeasure(14), () => new wickra.TradeSignAutocorrelation(10), () => new wickra.Pin(10)]) {
     const batch = make().batch(price, size, isBuy);
     const streamer = make();
     assert.equal(batch.length, n);
@@ -1279,6 +1280,16 @@ test('vpin / amihud / roll reference + streaming matches batch', () => {
       assert.ok((Number.isNaN(batch[i]) && s === null) || Math.abs(s - batch[i]) < 1e-9, `mismatch at ${i}`);
     }
   }
+  // Trade-sign autocorrelation: alternating signs -> -1, all buys -> +1.
+  let tsac = null;
+  const tsacInd = new wickra.TradeSignAutocorrelation(10);
+  for (let i = 0; i < 20; i++) tsac = tsacInd.update(100, 1, i % 2 === 0);
+  assert.ok(Math.abs(tsac - -1.0) < 1e-12);
+  // PIN: one-sided flow -> 1, balanced flow -> 0.
+  let pin = null;
+  const pinInd = new wickra.Pin(10);
+  for (let i = 0; i < 20; i++) pin = pinInd.update(100, 1, true);
+  assert.ok(Math.abs(pin - 1.0) < 1e-12);
 });
 
 test('price-impact indicators reference values', () => {