feat: add 9 Risk / Performance indicators (B18) (#218)

Adds nine risk/performance metrics to the existing **Risk / Performance** family, all consuming a per-period return series (`f64` in, `f64` out). Indicator count **498 → 507**.

## Indicators

Single-param (`new(period)`, macro bindings):
- **SterlingRatio** — mean return over average drawdown of the equity curve.
- **BurkeRatio** — return over root-sum-squared drawdowns.
- **MartinRatio** — Ulcer Performance Index; return over RMS percentage drawdown.
- **TailRatio** — 95th percentile over the absolute 5th percentile return.
- **KRatio** — Kestner; equity-curve OLS slope over the standard error of that slope.
- **CommonSenseRatio** — tail ratio times gain-to-pain.
- **GainToPainRatio** — sum of returns over the sum of absolute losses.

Multi-param (hand-written Python/Node bindings, variadic WASM macro):
- **UpsidePotentialRatio** — `new(period, mar)`; upside mean over downside deviation (Sortino philosophy).
- **M2Measure** — `new(period, risk_free, benchmark_stddev)`; Modigliani M², Sharpe rescaled into benchmark return units.

## Touchpoints
Core modules + unit tests, `mod.rs`/`lib.rs` wiring, Python/Node/WASM bindings (`index.d.ts`/`index.js` regenerated), fuzz drive lines, Python `SCALAR` registry + Node factories, CHANGELOG, and the indicator counters.

## Verification
- `cargo test -p wickra-core --lib` — 4149 passed
- `cargo test -p wickra-core --doc` — 457 passed
- `cargo clippy --workspace --all-targets --all-features -- -D warnings` — clean
- `npm test` (node) — 577 passed
- `pytest` (python) — 947 passed

bindings/node/src/lib.rs

@@ -245,9 +245,91 @@ node_scalar_indicator!(
     "UNIVERSALOSC",
     wc::UniversalOscillator
 );
+node_scalar_indicator!(SterlingRatioNode, "SterlingRatio", wc::SterlingRatio);
+node_scalar_indicator!(BurkeRatioNode, "BurkeRatio", wc::BurkeRatio);
+node_scalar_indicator!(MartinRatioNode, "MartinRatio", wc::MartinRatio);
+node_scalar_indicator!(TailRatioNode, "TailRatio", wc::TailRatio);
+node_scalar_indicator!(KRatioNode, "KRatio", wc::KRatio);
+node_scalar_indicator!(
+    CommonSenseRatioNode,
+    "CommonSenseRatio",
+    wc::CommonSenseRatio
+);
+node_scalar_indicator!(GainToPainRatioNode, "GainToPainRatio", wc::GainToPainRatio);
 
 // Multi-arg Ehlers scalars: hand-written (node_scalar_indicator! is single-period).
 
+#[napi(js_name = "UpsidePotentialRatio")]
+pub struct UpsidePotentialRatioNode {
+    inner: wc::UpsidePotentialRatio,
+}
+
+#[napi]
+impl UpsidePotentialRatioNode {
+    #[napi(constructor)]
+    pub fn new(period: u32, mar: f64) -> napi::Result<Self> {
+        Ok(Self {
+            inner: wc::UpsidePotentialRatio::new(period as usize, mar).map_err(map_err)?,
+        })
+    }
+    #[napi]
+    pub fn update(&mut self, value: f64) -> Option<f64> {
+        self.inner.update(value)
+    }
+    #[napi]
+    pub fn batch(&mut self, prices: Vec<f64>) -> Vec<f64> {
+        flatten(self.inner.batch(&prices))
+    }
+    #[napi]
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+    #[napi(js_name = "isReady")]
+    pub fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    #[napi(js_name = "warmupPeriod")]
+    pub fn warmup_period(&self) -> u32 {
+        self.inner.warmup_period() as u32
+    }
+}
+
+#[napi(js_name = "M2Measure")]
+pub struct M2MeasureNode {
+    inner: wc::M2Measure,
+}
+
+#[napi]
+impl M2MeasureNode {
+    #[napi(constructor)]
+    pub fn new(period: u32, risk_free: f64, benchmark_stddev: f64) -> napi::Result<Self> {
+        Ok(Self {
+            inner: wc::M2Measure::new(period as usize, risk_free, benchmark_stddev)
+                .map_err(map_err)?,
+        })
+    }
+    #[napi]
+    pub fn update(&mut self, value: f64) -> Option<f64> {
+        self.inner.update(value)
+    }
+    #[napi]
+    pub fn batch(&mut self, prices: Vec<f64>) -> Vec<f64> {
+        flatten(self.inner.batch(&prices))
+    }
+    #[napi]
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+    #[napi(js_name = "isReady")]
+    pub fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    #[napi(js_name = "warmupPeriod")]
+    pub fn warmup_period(&self) -> u32 {
+        self.inner.warmup_period() as u32
+    }
+}
+
 #[napi(js_name = "BANDPASS")]
 pub struct BandpassFilterNode {
     inner: wc::BandpassFilter,