C ABI: full example suite + docs & About coverage (#224)

Stacked on #222 (base `feat/c-abi-hub`), so the diff is just the additions on top of the hub foundation — no merge of #222 required.

## What this adds

**Examples — full parity with rust/python/node (`examples/c/`)**
- `streaming.c` upgraded to the multi-indicator (SMA/EMA/RSI/MACD + signals) demo
- `backtest.c`, `multi_timeframe.c` (manual time-bucket resampling), `parallel_assets.c` (serial vs OpenMP fan-out, one handle per asset)
- three educational strategies: `strategy_rsi_mean_reversion.c`, `strategy_macd_adx.c`, `strategy_bollinger_squeeze.c`
- two network examples shelling out to `curl`: `fetch_btcusdt.c`, `live_binance.c` (REST poll)
- two header-only helpers (`wickra_csv.h`, `wickra_strategy.h`) since the C ABI ships no IO layer
- CMake builds all 11; the 9 offline ones run under `ctest` on 3 OS; the network two are built-only

**Docs & metadata — surface the C ABI everywhere it was missing**
- ARCHITECTURE diagram + crate table, SECURITY + THREAT_MODEL (the C ABI as the sole `unsafe` FFI surface), the three binding package READMEs, issue/PR templates, CHANGELOG, and the GitHub About template (live About + org description updated too)

**Cleanup**
- removed all references to the private generator tooling from public files (`bindings/c/src/lib.rs` header, `CONTRIBUTING.md`, `sync-about.yml`)

Verified locally: `cargo build -p wickra-c --release`, `cmake + ctest` (9/9 pass), and `-Wall -Wextra -Wpedantic` clean on gcc 13.

SECURITY.md

@@ -58,7 +58,11 @@ artifacts, and (4) a healthy dependency supply chain.
 
 - *Memory safety* — the core and all bindings are written in Rust. The crates
   forbid or minimise `unsafe`, so the compiler guarantees memory and thread
-  safety for the indicator logic.
+  safety for the indicator logic. The one exception is the C ABI
+  ([`bindings/c`](bindings/c)), whose thin FFI shim is necessarily `unsafe`
+  because it dereferences caller-supplied pointers; it adds no indicator logic,
+  validates every handle for NULL, and never lets a panic cross the boundary, so
+  the safe core's guarantees still cover all computation.
 - *Input robustness* — every indicator validates its parameters and rejects
   non-finite inputs at construction; behaviour on edge cases (flat markets,
   warmup, reset) is pinned by unit tests, and the public update paths are