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.
kingchenc
67feec598a