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/CMakeLists.txt

@@ -8,6 +8,15 @@ if(NOT DEFINED WICKRA_LIB_DIR)
 endif()
 set(WICKRA_INCLUDE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../../bindings/c/include")
 
+# Absolute path to the bundled OHLCV datasets, baked into the data-driven
+# examples as a compile definition so they run from any working directory (the
+# C counterpart of the Rust examples' CARGO_MANIFEST_DIR).
+get_filename_component(WICKRA_DATA_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../data" ABSOLUTE)
+
+# OpenMP is optional: parallel_assets links it when present and falls back to a
+# single-threaded run otherwise.
+find_package(OpenMP QUIET)
+
 # Pick the right link target per platform/toolchain.
 #  - MSVC links the generated import library (wickra.dll.lib).
 #  - MinGW/gcc on Windows links the DLL directly.
@@ -27,12 +36,15 @@ endif()
 
 enable_testing()
 
-# Build one example, link it to the Wickra library, run it as a ctest. On Windows
-# the DLL is copied next to the executable so the loader finds it at run time.
-function(add_wickra_example name source)
+# Build one example and link it to the Wickra library. On Windows the DLL is
+# copied next to the executable so the loader finds it at run time. With
+# register_test=TRUE the example is also run as a ctest; network examples pass
+# FALSE (they are built only, never run in CI).
+function(add_wickra_example name source register_test)
     add_executable(${name} ${source})
     target_include_directories(${name} PRIVATE "${WICKRA_INCLUDE_DIR}")
     target_link_libraries(${name} PRIVATE "${WICKRA_LINK_LIB}")
+    target_compile_definitions(${name} PRIVATE "WICKRA_DATA_DIR=\"${WICKRA_DATA_DIR}\"")
     if(UNIX AND NOT APPLE)
         target_link_libraries(${name} PRIVATE m)
     endif()
@@ -41,13 +53,30 @@ function(add_wickra_example name source)
             COMMAND ${CMAKE_COMMAND} -E copy_if_different
                     "${WICKRA_RUNTIME}" "$<TARGET_FILE_DIR:${name}>")
     endif()
-    add_test(NAME ${name} COMMAND ${name})
-    if(NOT WIN32)
-        set_tests_properties(${name} PROPERTIES
-            ENVIRONMENT "LD_LIBRARY_PATH=${WICKRA_LIB_DIR};DYLD_LIBRARY_PATH=${WICKRA_LIB_DIR}")
+    if(register_test)
+        add_test(NAME ${name} COMMAND ${name})
+        if(NOT WIN32)
+            set_tests_properties(${name} PROPERTIES
+                ENVIRONMENT "LD_LIBRARY_PATH=${WICKRA_LIB_DIR};DYLD_LIBRARY_PATH=${WICKRA_LIB_DIR}")
+        endif()
     endif()
 endfunction()
 
-add_wickra_example(smoke smoke.c)         # links the boundary, asserts values
-add_wickra_example(streaming streaming.c) # runnable streaming demo
-add_wickra_example(cpp_smoke smoke.cpp)   # C++ RAII wrapper (wickra.hpp)
+# Offline examples — built and run as ctests.
+add_wickra_example(smoke smoke.c TRUE)                 # links the boundary, asserts values
+add_wickra_example(streaming streaming.c TRUE)         # multi-indicator tick stream
+add_wickra_example(cpp_smoke smoke.cpp TRUE)           # C++ RAII wrapper (wickra.hpp)
+add_wickra_example(backtest backtest.c TRUE)           # indicator basket over a CSV
+add_wickra_example(multi_timeframe multi_timeframe.c TRUE)  # resample + per-TF indicators
+add_wickra_example(parallel_assets parallel_assets.c TRUE)  # serial vs OpenMP fan-out
+add_wickra_example(strategy_rsi_mean_reversion strategy_rsi_mean_reversion.c TRUE)
+add_wickra_example(strategy_macd_adx strategy_macd_adx.c TRUE)
+add_wickra_example(strategy_bollinger_squeeze strategy_bollinger_squeeze.c TRUE)
+
+if(OpenMP_C_FOUND)
+    target_link_libraries(parallel_assets PRIVATE OpenMP::OpenMP_C)
+endif()
+
+# Network examples — built (so they stay compilable) but not run in CI.
+add_wickra_example(fetch_btcusdt fetch_btcusdt.c FALSE) # downloads CSVs via curl
+add_wickra_example(live_binance live_binance.c FALSE)   # polls Binance REST via curl