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/system/pisysteminfo.cpp

@@ -207,11 +207,19 @@ PIVector<PISystemInfo::MountInfo> PISystemInfo::mountInfo(bool ignore_cache) {
 PIString confDir() {
 	return
 #ifdef WINDOWS
+#  ifndef PIP_NO_FILESYSTEM
 		PIDir::home().path() + "/AppData/Local"
+#  else
+		""
+#  endif
 #elif defined(ANDROID)
 		""
 #else
+#  ifndef PIP_NO_FILESYSTEM
 		PIDir::home().path() + "/.config"
+#  else
+		""
+#  endif
 #endif
 		;
 }
@@ -234,11 +242,13 @@ PIString PISystemInfo::machineKey() {
 		PISystemInfo * si = instance();
 		PIByteArray salt;
 		PIString conf = confDir() + "/.pip_machine_salt";
+#ifndef PIP_NO_FILESYSTEM
 		if (PIFile::isExists(conf)) salt = PIFile::readAll(conf);
 		if (salt.size_s() != SALT_SIZE) {
 			salt = generateSalt();
 			PIFile::writeAll(conf, salt);
 		}
+#endif
 		ret = si->OS_name + "_" + si->architecture + "_" + si->hostname + "_" + salt.toHex();
 	}
 	return ret;