fix(app,ci): set CMAKE_POLICY_VERSION_MINIMUM=3.5 for fetched deps (#26)

The "Build Desktop App (CMake)" CI job began failing at Configure with:

  CMake Error at build/_deps/cjson-src/CMakeLists.txt:2 (cmake_minimum_required):
    Compatibility with CMake < 3.5 has been removed from CMake.

cJSON v1.7.18 (fetched via FetchContent) still declares a pre-3.5
cmake_minimum_required. The GitHub Windows runner upgraded to the CMake that
ships with Visual Studio 2026 (CMake >= 4.0), which removed compatibility with
that old policy version, so configuration aborts before any of our code builds.

Set CMAKE_POLICY_VERSION_MINIMUM=3.5 before FetchContent so the fetched
subprojects adopt a still-supported policy floor. The variable is read by each
subproject's cmake_minimum_required and is silently ignored on CMake < 3.31,
so local builds on older toolchains are unaffected. No functional change.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: knaufinator

app/CMakeLists.txt

@@ -4,6 +4,13 @@ project(stewart-platform LANGUAGES C CXX)
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
+# Some fetched deps (e.g. cJSON v1.7.18) still declare cmake_minimum_required
+# < 3.5, which CMake >= 4.0 (the VS 2026 CI runner) rejects outright. Provide a
+# compatible policy floor so those subprojects still configure. This variable is
+# read by each subproject's cmake_minimum_required; it is silently ignored on
+# CMake < 3.31, so it is safe for older local toolchains too.
+set(CMAKE_POLICY_VERSION_MINIMUM 3.5)
+
 # ── Fetch dependencies ──────────────────────────────────────────────
 include(FetchContent)