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.

examples/c/wickra_csv.h

@@ -0,0 +1,90 @@
+/* Shared OHLCV CSV loader for the Wickra C examples.
+ *
+ * The C ABI exposes only the indicators, not the wickra-data IO layer, so the
+ * examples read CSV themselves. This header-only helper is the C counterpart of
+ * `wickra_data::csv::CandleReader` used by the Rust examples: it parses the
+ * standard `timestamp,open,high,low,close,volume` files shipped under
+ * `examples/data/`.
+ *
+ * Header-only: define WICKRA_CSV_IMPL in exactly one translation unit (each
+ * example is a single .c file, so it just defines it before including this).
+ */
+#ifndef WICKRA_CSV_H
+#define WICKRA_CSV_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct WickraCandle {
+    int64_t timestamp;
+    double open;
+    double high;
+    double low;
+    double close;
+    double volume;
+} WickraCandle;
+
+/* Load an OHLCV CSV into a malloc'd array. Returns the candle count and stores
+ * the array in *out (caller frees with free()). Returns 0 and leaves *out NULL
+ * on any error (missing file, no parseable rows). A leading header line whose
+ * first field is non-numeric is skipped. */
+size_t wickra_load_csv(const char *path, WickraCandle **out);
+
+#ifdef WICKRA_CSV_IMPL
+
+#include <stdio.h>
+#include <stdlib.h>
+
+size_t wickra_load_csv(const char *path, WickraCandle **out) {
+    *out = NULL;
+    FILE *f = fopen(path, "r");
+    if (f == NULL) {
+        fprintf(stderr, "wickra_load_csv: cannot open %s\n", path);
+        return 0;
+    }
+
+    size_t cap = 1024;
+    size_t n = 0;
+    WickraCandle *rows = (WickraCandle *)malloc(cap * sizeof(*rows));
+    if (rows == NULL) {
+        fclose(f);
+        return 0;
+    }
+
+    char line[512];
+    while (fgets(line, (int)sizeof(line), f) != NULL) {
+        WickraCandle c;
+        long long ts = 0;
+        /* sscanf returns the number of fields successfully matched. A header
+         * row ("timestamp,...") matches 0 and is skipped. */
+        int matched = sscanf(line, "%lld,%lf,%lf,%lf,%lf,%lf", &ts, &c.open,
+                             &c.high, &c.low, &c.close, &c.volume);
+        if (matched != 6) {
+            continue;
+        }
+        c.timestamp = (int64_t)ts;
+
+        if (n == cap) {
+            cap *= 2;
+            WickraCandle *grown = (WickraCandle *)realloc(rows, cap * sizeof(*rows));
+            if (grown == NULL) {
+                free(rows);
+                fclose(f);
+                return 0;
+            }
+            rows = grown;
+        }
+        rows[n++] = c;
+    }
+    fclose(f);
+
+    if (n == 0) {
+        free(rows);
+        return 0;
+    }
+    *out = rows;
+    return n;
+}
+
+#endif /* WICKRA_CSV_IMPL */
+#endif /* WICKRA_CSV_H */