fix: build errors — nlohmann include path, fn_log printf style, crypt32 link

- Fix nlohmann include: 'vendor/nlohmann/json.hpp' -> 'nlohmann/json.hpp'
  (cpp/vendor is in include path, no double-vendor prefix needed)
- Fix fn_log API: log_info/log_warn/log_error (not info/warn/error)
- Fix format strings: {} -> %s (logger uses printf-style, not fmtlib)
- CMakeLists: add crypt32 link for Windows DPAPI (MinGW needs explicit link,
  #pragma comment(lib) only works with MSVC)
- Build: exit 0, exe 22MB, .rsrc section present (icon embedded)

Issue: 0129
Co-Authored-By: fn-orquestador <noreply@fn-registry.local>

CMakeLists.txt

@@ -19,4 +19,6 @@ endif()
 
 if(WIN32)
     set_target_properties(agents_dashboard PROPERTIES WIN32_EXECUTABLE TRUE)
+    # secret_store.cpp uses CryptProtectData / CryptUnprotectData (crypt32)
+    target_link_libraries(agents_dashboard PRIVATE crypt32)
 endif()