build: replace brew find_package with FetchContent for fmt and spdlog

Removes the Homebrew dependency so the build works on any platform
with only CMake 3.24+ and a C++20 compiler. fmt and spdlog are now
fetched and compiled from source alongside the other FetchContent deps.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CMakeLists.txt

@@ -8,18 +8,20 @@ set(CMAKE_CXX_EXTENSIONS OFF)
 # All executables land in build/bin so studio-manager finds node binaries next to itself
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 
-# Homebrew on Apple Silicon
-if(APPLE)
-    list(APPEND CMAKE_PREFIX_PATH /opt/homebrew)
-endif()
-
 include(FetchContent)
 
-# ── fmt (brew install fmt — already installed) ───────────────────────────────
-find_package(fmt REQUIRED)
+# ── fmt ──────────────────────────────────────────────────────────────────────
+FetchContent_Declare(fmt
+    GIT_REPOSITORY https://github.com/fmtlib/fmt.git
+    GIT_TAG        12.1.0)
+FetchContent_MakeAvailable(fmt)
 
-# ── spdlog (brew install spdlog — just installed) ────────────────────────────
-find_package(spdlog REQUIRED)
+# ── spdlog (uses the fmt target fetched above) ────────────────────────────────
+set(SPDLOG_FMT_EXTERNAL ON CACHE BOOL "" FORCE)
+FetchContent_Declare(spdlog
+    GIT_REPOSITORY https://github.com/gabime/spdlog.git
+    GIT_TAG        v1.17.0)
+FetchContent_MakeAvailable(spdlog)
 
 # ── stduuid (header-only; no brew formula) ───────────────────────────────────
 set(UUID_SYSTEM_GENERATOR ON  CACHE BOOL "" FORCE)  # use CoreFoundation on macOS