refactor: migrate MICRO_PIP to fine-grained feature flags

Replace monolithic MICRO_PIP/PIP_MICRO with granular flags:

Feature flags (CMake options + platform auto-detection):
- PIP_NO_FILESYSTEM, PIP_NO_THREADS, PIP_NO_SOCKET
- PIP_NO_PROCESS, PIP_NO_DYNLIB, PIP_NO_FFT, PIP_NO_SERIAL

Embedded optimization flag:
- PIP_EMBEDDED (auto-set for Pico SDK and FreeRTOS)
  Controls buffer sizes, time stubs, terminal fallback, init stubs

Platform blocks in CMakeLists.txt:
- Pico SDK: auto-disables FS, PROCESS, DYNLIB, FFT, SERIAL;
  conditionally disables THREADS (no FreeRTOS) and SOCKET (no LWIP)
- FreeRTOS: auto-disables FS, PROCESS, DYNLIB, FFT, SERIAL;
  conditionally disables SOCKET (no LWIP)
- Android: auto-disables PROCESS, DYNLIB, FFT

Updated 96 files across libs/, utils/, tests/, and CMakeLists.txt.
Builds verified for Linux (547 tests pass) and Pico SDK (100%).
Removed all MICRO_PIP and PIP_MICRO references (0 remaining).

libs/main/thread/pimutex.h

@@ -95,4 +95,28 @@ private:
 };
 
 #endif // PIP_NO_THREADS
+
+#ifdef PIP_NO_THREADS
+//! \~\ingroup Thread
+//! \~\brief
+//! \~english Dummy mutex for builds without threading support.
+//! \~russian Заглушка мьютекса для сборки без поддержки потоков.
+class PIMutex {
+public:
+	void lock() {}
+	void unlock() {}
+	bool tryLock() { return true; }
+	void * handle() { return nullptr; }
+};
+
+//! \~\ingroup Thread
+//! \~\brief
+//! \~english Dummy mutex locker for builds without threading support.
+//! \~russian Заглушка блокировщика для сборки без поддержки потоков.
+class PIMutexLocker {
+public:
+	PIMutexLocker(PIMutex &, bool = true) {}
+};
+#endif // PIP_NO_THREADS
+
 #endif // PIMUTEX_H