feat(indicators): add B6 Bands & Channels family (429 -> 434) (#191)

Adds the **B6 Bands & Channels** batch — five band/channel indicators, taking the catalogue from 429 to 434.

| Indicator | Input → Output | Summary |
|-----------|----------------|---------|
| `ProjectionBands` | `Candle` → `{upper,middle,lower}` | Widner forward-projected high/low regression envelope |
| `ProjectionOscillator` | `Candle` → `f64` | Close position inside the projection bands, scaled 0..100 |
| `QuartileBands` | `f64` → `{upper,middle,lower}` | Rolling 25th/50th/75th-percentile (Q1/median/Q3) envelope |
| `BomarBands` | `f64` → `{upper,middle,lower}` | Adaptive percentage bands containing a target coverage fraction of recent closes |
| `MedianChannel` | `f64` → `{upper,middle,lower}` | Robust median ± multiplier·MAD envelope |

All five are distinct from existing indicators (verified against the core: `LinRegChannel`, `StandardErrorBands`, `Donchian`, `RollingQuantile`, `HurstChannel`). SKIPped from the roadmap: Price Channel (= `Donchian`) and Moving-Average Channel (≈ `MaEnvelope`/`Keltner`).

Each ships:
- Core indicator with per-branch unit tests (Codecov-strict 100%).
- python / node / wasm bindings (struct outputs are hand-written; `ProjectionOscillator` uses the generated candle→f64 path).
- Fuzz drives, python (`MULTI`/`SCALAR_MULTI`/`CANDLE_SCALAR`) + node test registries, README + CHANGELOG counter bump to 434.

Verified locally: `cargo fmt`, `clippy --workspace --all-targets --all-features -D warnings` (clean), `wickra-core` 3511 lib + 392 doc tests, node 509 tests, pytest 840.

bindings/node/__tests__/indicators.test.js

@@ -355,6 +355,7 @@ const candleScalar = {
   TTM_TREND: { make: () => new wickra.TTM_TREND(6), step: (ind, i) => ind.update(high[i], low[i], close[i]), batch: (ind) => ind.batch(high, low, close) },
   Qstick: { make: () => new wickra.Qstick(10), step: (ind, i) => ind.update(open[i], close[i]), batch: (ind) => ind.batch(open, close) },
   VolatilityRatio: { make: () => new wickra.VolatilityRatio(14), step: (ind, i) => ind.update(high[i], low[i], close[i]), batch: (ind) => ind.batch(high, low, close) },
+  ProjectionOscillator: { make: () => new wickra.ProjectionOscillator(14), step: (ind, i) => ind.update(high[i], low[i], close[i]), batch: (ind) => ind.batch(high, low, close) },
 };
 
 for (const [name, d] of Object.entries(candleScalar)) {
@@ -442,6 +443,10 @@ const multi = {
   GatorOscillator: { make: () => new wickra.GatorOscillator(13, 8, 5), fields: ['upper', 'lower'], step: (ind, i) => ind.update(high[i], low[i], close[i]), batch: (ind) => ind.batch(high, low, close) },
   KasePermissionStochastic: { make: () => new wickra.KasePermissionStochastic(9, 3), fields: ['fast', 'slow'], step: (ind, i) => ind.update(high[i], low[i], close[i]), batch: (ind) => ind.batch(high, low, close) },
   VolatilityCone: { make: () => new wickra.VolatilityCone(20, 60), fields: ['current', 'min', 'median', 'max', 'percentile'], step: (ind, i) => ind.update(high[i], low[i], close[i]), batch: (ind) => ind.batch(high, low, close) },
+  QuartileBands: { make: () => new wickra.QuartileBands(4), fields: ['upper', 'middle', 'lower'], step: (ind, i) => ind.update(close[i]), batch: (ind) => ind.batch(close) },
+  BomarBands: { make: () => new wickra.BomarBands(4, 0.85), fields: ['upper', 'middle', 'lower'], step: (ind, i) => ind.update(close[i]), batch: (ind) => ind.batch(close) },
+  MedianChannel: { make: () => new wickra.MedianChannel(5, 2.0), fields: ['upper', 'middle', 'lower'], step: (ind, i) => ind.update(close[i]), batch: (ind) => ind.batch(close) },
+  ProjectionBands: { make: () => new wickra.ProjectionBands(3), fields: ['upper', 'middle', 'lower'], step: (ind, i) => ind.update(high[i], low[i]), batch: (ind) => ind.batch(high, low) },
 };
 
 for (const [name, d] of Object.entries(multi)) {