Add C# (.NET) binding over the C ABI hub (#226)

The first language stecker on the C ABI hub: a .NET binding exposing all 514
indicators as idiomatic `IDisposable` classes, generated from `wickra.h`.

## What's here

- **`bindings/csharp/`** — the `Wickra` .NET 8 package. `[LibraryImport]`
  source-generated P/Invoke (`NativeMethods.g.cs`) plus idiomatic wrappers
  (`Indicators.g.cs`), both generated from the committed `bindings/c/include/wickra.h`.
  The binding owns no indicator maths — it only marshals types across the C ABI.
- **Marshalling, verified end-to-end against the native library.** Opaque handles
  cross as `nint` kept alive per call via a `SafeHandle`; `bool` as
  `[MarshalAs(U1)]` (Rust `bool` is one byte); a self-correcting
  `DllImportResolver` validates the loaded library actually exports the Wickra
  ABI. Tests cover one representative per FFI archetype (scalar, candle, pairwise,
  multi-output, bars, profile, values-profile, order-book / array-input) plus
  exact Sma reference values.
- **NuGet packaging** — `dotnet pack` produces `Wickra.<version>.nupkg`; the
  release pipeline stages prebuilt native libraries under `runtimes/<rid>/native/`
  for six target triples (win/linux/osx × x64/arm64).
- **`examples/csharp/`** — nine examples mirroring `examples/c/`: streaming,
  backtest, multi_timeframe, parallel_assets, three strategies, and
  fetch_btcusdt + live_binance.
- **CI** — a `csharp` job on the three OSes builds the C ABI, tests the binding,
  and runs the offline examples. **Release** — a gated `csharp-publish` job packs
  and pushes to NuGet (gated on `NUGET_API_KEY`, independent of the GitHub-release
  job so a C# hiccup never blocks the C/C++ asset release).
- **Docs consistency wave** — README, CONTRIBUTING, CHANGELOG, examples/README,
  the issue / PR templates, `sync-about.yml`, and `.gitattributes`.

The native Python / Node / WASM bindings and the C ABI are untouched; this is
additive. Publishing to NuGet stays gated behind the release tag and the secret.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -30,9 +30,9 @@ assignees: ""
 ## Environment
 
 - Wickra version:
-- Language / binding: <!-- Rust crate / Python / Node / WASM / C ABI -->
+- Language / binding: <!-- Rust crate / Python / Node / WASM / C ABI / C# (.NET) -->
 - OS and architecture:
-- Rust / Python / Node version (If relevant):
+- Rust / Python / Node / .NET version (If relevant):
 
 ## Additional context
 

.github/ISSUE_TEMPLATE/bug_report_detailed.md

@@ -26,7 +26,7 @@ assignees: []
 | Binding version      | `e.g. python 0.4.2 / node 0.4.2`       |
 | OS / arch            | `e.g. Windows 11 x86_64, Linux glibc`  |
 | Rust toolchain       | `rustc --version` (If building from source) |
-| Python / Node version | `python --version` / `node --version` |
+| Python / Node / .NET version | `python --version` / `node --version` / `dotnet --version` |
 
 ## Minimal reproducer
 

.github/ISSUE_TEMPLATE/feature_request.md

@@ -25,6 +25,8 @@ assignees: ""
 - [ ] Should be exposed in the Python binding
 - [ ] Should be exposed in the Node binding
 - [ ] Should be exposed in the WASM binding
+- [ ] Should be exposed in the C ABI
+- [ ] Should be exposed in the C# / .NET binding
 
 ## Additional context
 

.github/ISSUE_TEMPLATE/performance_regression.md

@@ -13,7 +13,7 @@ assignees: []
 ## Affected code path
 
 - Indicator / API: `e.g. EMA.update`
-- Binding: `Rust / Python / Node / Wasm / C ABI`
+- Binding: `Rust / Python / Node / Wasm / C ABI / C# (.NET)`
 - Hot loop or one-shot call?
 
 ## Versions compared

.github/ISSUE_TEMPLATE/question.md

@@ -33,4 +33,4 @@ import wickra as ta
 ## Environment (Only if relevant)
 
 - Wickra version: `e.g. 0.4.2`
-- Binding: `Rust / Python / Node / Wasm / C ABI`
+- Binding: `Rust / Python / Node / Wasm / C ABI / C# (.NET)`