fix(build): revert NDK to 27.3.13750724

NDK 29's Clang-21 libc++ makes libTEESimulator.so reference
__cxa_init_primary_exception, which the platform libc++ inside
keystore2 does not export. The injected lib resolves its C++ ABI
symbols against the target process at dlopen time, so injection
failed with "cannot locate symbol" on every retry. keystore2 ran
unhooked and every app saw the raw TEE chain (KeyAttestation showed
the real unlocked bootloader; per-UID NDJSON never created).

libc++ began emitting that symbol from std::exception_ptr
construction in Clang 19, so 27.3 (Clang 18) is the last toolchain
that builds a loadable lib. The exception_ptr machinery enters via
the AOSP/binder stub headers, not module code.

Verified on device: lib injects (3 maps in keystore2), KeyAttestation
generateKey -> PATCH with deviceLocked=true, verifiedBootState=Verified.

app/build.gradle.kts

@@ -35,7 +35,7 @@ val verName = "v6.0.1"
 android {
     namespace = "org.matrix.TEESimulator"
     compileSdk = 36
-    ndkVersion = "29.0.14206865"
+    ndkVersion = "27.3.13750724"
     buildToolsVersion = "36.0.0"
 
     defaultConfig {